libxtables: prefix/order - move check_inverse to xtables.c

This also adds a warning that intrapositional negation support
is deprecated.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/extensions/libipt_SNAT.c b/extensions/libipt_SNAT.c
index 0780aa1..96ef56e 100644
--- a/extensions/libipt_SNAT.c
+++ b/extensions/libipt_SNAT.c
@@ -152,7 +152,7 @@
 
 	switch (c) {
 	case '1':
-		if (check_inverse(optarg, &invert, NULL, 0))
+		if (xtables_check_inverse(optarg, &invert, NULL, 0))
 			exit_error(PARAMETER_PROBLEM,
 				   "Unexpected `!' after --to-source");