Put xtables.c into its own library, libxtables.so

iproute2's tc's m_ipt.c poses as a pseudo-iptables program to make
use of the info structure composition of iptables extensions.
Since tc would have to clone a lot of code, xtables.c is put into
its own shared library and should not be relied upon by any other
programs.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/.gitignore b/.gitignore
index 9ebe15c..741f972 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,11 +1,14 @@
 .*.d
 .*.dd
 *.a
+*.la
+*.lo
 *.oo
 *.so
 *.o
 .deps
 .dirstamp
+.libs
 Makefile
 Makefile.in
 
@@ -31,6 +34,7 @@
 /ltmain.sh
 /missing
 /stamp-h1
+/xtables.pc
 
 /ip6tables
 /ip6tables.8