netfilter: xtables: change xt_target.checkentry return type

Restore function signatures from bool to int so that we can report
memory allocation failures or similar using -ENOMEM rather than
always having to pass -EINVAL back.

// <smpl>
@@
type bool;
identifier check, par;
@@
-bool check
+int check
 (struct xt_tgchk_param *par) { ... }
// </smpl>

Minus the change it does to xt_ct_find_proto.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/net/ipv4/netfilter/arpt_mangle.c b/net/ipv4/netfilter/arpt_mangle.c
index b0d5b1d..4b51a02 100644
--- a/net/ipv4/netfilter/arpt_mangle.c
+++ b/net/ipv4/netfilter/arpt_mangle.c
@@ -54,7 +54,7 @@
 	return mangle->target;
 }
 
-static bool checkentry(const struct xt_tgchk_param *par)
+static int checkentry(const struct xt_tgchk_param *par)
 {
 	const struct arpt_mangle *mangle = par->targinfo;