libiptc: resolve compile failure

  CC     libip4tc.lo
In file included from libip4tc.c:118:0:
libiptc.c:70:8: error: redefinition of "struct xt_error_target"
../include/linux/netfilter/x_tables.h:69:8: note: originally defined here

Remove libiptc's duplicate definition and substitute names.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
1 file changed