ipfw: avoid critical error for broadcast

In some setup, suricata may receive broadcast packets and the call
to sendto may fail if the wrong interface is choosen by kernel.
This patch change the error treatment to avoid to leave when
this problem occurs.

src/source-ipfw.c

@@ -634,9 +634,16 @@ TmEcode IPFWSetVerdict(ThreadVars *tv, IPFWThreadVars *ptv, Packet *p)
 
         IPFWMutexLock(nq);
         if (sendto(nq->fd, GET_PKT_DATA(p), GET_PKT_LEN(p), 0,(struct sockaddr *)&nq->ipfw_sin, nq->ipfw_sinlen) == -1) {
-            SCLogWarning(SC_WARN_IPFW_XMIT,"Write to ipfw divert socket failed: %s",strerror(errno));
-            IPFWMutexUnlock(nq);
-            SCReturnInt(TM_ECODE_FAILED);
+            int r = errno;
+            switch (r) {
+                default:
+                    SCLogWarning(SC_WARN_IPFW_XMIT,"Write to ipfw divert socket failed: %s",strerror(r));
+                    IPFWMutexUnlock(nq);
+                    SCReturnInt(TM_ECODE_FAILED);
+                case EHOSTDOWN:
+                case ENETDOWN:
+                    break;
+            }
         }
 
         IPFWMutexUnlock(nq);