configure: Link with ip4tc and ip6tc, too.

This solves this problem:

octo@leeloo:/tmp $ gcc -o conftest -g -O2     conftest.c -liptc -ldl
/usr/bin/ld: /tmp/ccuJEDqP.o: undefined reference to symbol 'iptc_init'
/usr/bin/ld: note: 'iptc_init' is defined in DSO /lib64/libip4tc.so.0 so try adding it to the linker command line
/lib64/libip4tc.so.0: could not read symbols: Invalid operation
collect2: ld returned 1 exit status

Why the iptables plugin compiles without this is beyond me.

Change-Id: If615bee0c9524d907ca1834d5c337ed50c625c5b