configure: fallback to libpcap on Windows

If npcap/wpcap is not found on Windows, try libpcap. This allows
Suricata to build without NPCap on Windows, however live capture won't
be available.

configure.ac

@@ -278,7 +278,6 @@
 
     e_magic_file=""
     e_magic_file_comment="#"
-    PCAP_LIB_NAME="pcap"
     case "$host" in
         *-*-*freebsd*)
             LUA_LIB_NAME="lua-5.1"
@@ -308,14 +307,14 @@
         *-*-mingw32*|*-*-msys)
             CFLAGS="${CFLAGS} -DOS_WIN32"
             WINDOWS_PATH="yes"
-            PCAP_LIB_NAME="wpcap"
             AC_DEFINE([HAVE_NON_POSIX_MKDIR], [1], [mkdir is not POSIX compliant: single arg])
             RUST_LDADD=" -lws2_32 -liphlpapi -lwbemuuid -lOle32 -lOleAut32 -lUuid -luserenv -lshell32 -ladvapi32 -lgcc_eh -lbcrypt"
+            TRY_WPCAP="yes"
             ;;
         *-*-cygwin)
             LUA_LIB_NAME="lua"
             WINDOWS_PATH="yes"
-            PCAP_LIB_NAME="wpcap"
+            TRY_WPCAP="yes"
             ;;
         *-*-solaris*)
             AC_MSG_WARN([support for Solaris/Illumos/SunOS is experimental])
@@ -1176,38 +1175,36 @@
                 #define _DEFAULT_SOURCE 1
             ]])
 
-    LIBPCAP=""
-    PKG_CHECK_MODULES([PCAP],libpcap,[CPPFLAGS="${CPPFLAGS} ${PCAP_CFLAGS}" LIBS="${LIBS} ${PCAP_LIBS}"],[:])
-    AC_CHECK_LIB(${PCAP_LIB_NAME}, pcap_open_live,, LIBPCAP="no")
-    if test "$LIBPCAP" = "no"; then
-        echo
-        echo "   ERROR!  libpcap library not found, go get it"
-        echo "   from http://www.tcpdump.org or your distribution:"
-        echo
-        echo "   Ubuntu: apt-get install libpcap-dev"
-        echo "   Fedora: dnf install libpcap-devel"
-        echo "   CentOS/RHEL: yum install libpcap-devel"
-        echo
-        exit 1
+    have_wpcap=""
+    if test "$TRY_WPCAP" = "yes"; then
+        AC_CHECK_LIB(wpcap, pcap_activate, [], have_wpcap="no")
+        if test "$have_wpcap" = "no"; then
+            echo ""
+            echo "    Warning: NPCap was not found. Live capture will not be available."
+            echo ""
+        else
+            PCAP_LIB_NAME="wpcap"
+            have_wpcap="yes"
+        fi
     fi
 
-    # pcap_activate and pcap_create only exists in libpcap >= 1.0
-    LIBPCAPVTEST=""
-    #To prevent duping the lib link we reset LIBS after this check. Setting action-if-found to NULL doesn't seem to work
-    #see: http://blog.flameeyes.eu/2008/04/29/i-consider-ac_check_lib-harmful
-    TMPLIBS="${LIBS}"
-    AC_CHECK_LIB(${PCAP_LIB_NAME}, pcap_activate,, LPCAPVTEST="no")
-    if test "$LPCAPVTEST" = "no"; then
-        echo
-        echo "   ERROR!  libpcap library too old, need at least 1+, "
-        echo "   go get it from http://www.tcpdump.org or your distribution:"
-        echo
-        echo "   Ubuntu: apt-get install libpcap-dev"
-        echo "   Fedora: dnf install libpcap-devel"
-        echo "   CentOS/RHEL: yum install libpcap-devel"
-        echo
-        exit 1
+    if test "$have_wpcap" != "yes"; then
+        AC_CHECK_LIB(pcap, pcap_open_dead, [], [
+            echo
+            echo "   ERROR!  libpcap library not found, go get it"
+            echo "   from http://www.tcpdump.org or your distribution:"
+            echo
+            echo "   Ubuntu: apt-get install libpcap-dev"
+            echo "   Fedora: dnf install libpcap-devel"
+            echo "   CentOS/RHEL: yum install libpcap-devel"
+            echo
+            exit 1
+        ])
+        PCAP_LIB_NAME="pcap"
     fi
+
+    PKG_CHECK_MODULES([PCAP],libpcap,[CPPFLAGS="${CPPFLAGS} ${PCAP_CFLAGS}" LIBS="${LIBS} ${PCAP_LIBS}"],[:])
+
     AC_PATH_PROG(HAVE_PCAP_CONFIG, pcap-config, "no")
     if test "$HAVE_PCAP_CONFIG" = "no" -o "$cross_compiling" = "yes"; then
         AC_MSG_RESULT(no pcap-config is use)
@@ -1215,7 +1212,6 @@
         PCAP_CFLAGS="$(pcap-config --defines) $(pcap-config --cflags)"
         AC_SUBST(PCAP_CFLAGS)
     fi
-    LIBS="${TMPLIBS}"
 
     #Appears as if pcap_set_buffer_size is linux only?
     LIBPCAPSBUFF=""