tftp: StringToAppProto case

So, fuzz_applayerparserparse_tftp will fuzz tftp

(cherry picked from commit c9d664b0a0)

src/app-layer-protos.c

@@ -142,6 +142,8 @@ AppProto StringToAppProto(const char *proto_name)
     if (strcmp(proto_name,"ftp")==0) return ALPROTO_FTP;
     if (strcmp(proto_name, "ftp-data") == 0)
         return ALPROTO_FTPDATA;
+    if (strcmp(proto_name, "tftp") == 0)
+        return ALPROTO_TFTP;
     if (strcmp(proto_name,"smtp")==0) return ALPROTO_SMTP;
     if (strcmp(proto_name,"tls")==0) return ALPROTO_TLS;
     if (strcmp(proto_name,"ssh")==0) return ALPROTO_SSH;