build: remove symlink-only extensions from static object list

$ ./configure --enable-static --disable-shared --enable-ipv4
  --enable-ipv6 && make
[...]
make[3]: *** No rule to make target "libxt_NOTRACK.o", needed by
"libext.a". Stop.

Signed-off-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
1 file changed