Autoconf: Avoid incorrectly include the libpcap's config.h

Fix the problem when configure like following is done:
./configure CFLAGS='-I../libpcap -I.'
This gives:
CCOPT =  -I../libpcap -I. -W -Wall [...]

See also the GitHub bug report #1313.

In Makefile.in, there is:
INCLS = -I. @V_INCLS@

Put $(INCLS) first in FULL_CFLAGS.

Author: fxlb

Makefile.in

@@ -49,7 +49,7 @@ DEFS = @DEFS@ @CPPFLAGS@ @V_DEFS@
 
 # Standard CFLAGS
 CFLAGS = @CFLAGS@
-FULL_CFLAGS = $(CCOPT) $(DEFS) $(INCLS) $(CFLAGS)
+FULL_CFLAGS = $(INCLS) $(CCOPT) $(DEFS) $(CFLAGS)
 
 # Standard LDFLAGS
 LDFLAGS = @LDFLAGS@