libiptc: use a family-invariant xtc_ops struct for code reduction

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/libiptc/libip6tc.c b/libiptc/libip6tc.c
index 9febee3..7128e1c 100644
--- a/libiptc/libip6tc.c
+++ b/libiptc/libip6tc.c
@@ -88,6 +88,7 @@
 #define TC_STRERROR		ip6tc_strerror
 #define TC_NUM_RULES		ip6tc_num_rules
 #define TC_GET_RULE		ip6tc_get_rule
+#define TC_OPS			ip6tc_ops
 
 #define TC_AF			AF_INET6
 #define TC_IPPROTO		IPPROTO_IPV6