netfilter: xtables: change xt_match.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.

This semantic patch may not be too precise (checking for functions
that use xt_mtchk_param rather than functions referenced by
xt_match.checkentry), but reviewed, it produced the intended result.

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

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/net/netfilter/xt_dscp.c b/net/netfilter/xt_dscp.c
index 6ecedc1..295da4c 100644
--- a/net/netfilter/xt_dscp.c
+++ b/net/netfilter/xt_dscp.c
@@ -42,7 +42,7 @@
 	return (dscp == info->dscp) ^ !!info->invert;
 }
 
-static bool dscp_mt_check(const struct xt_mtchk_param *par)
+static int dscp_mt_check(const struct xt_mtchk_param *par)
 {
 	const struct xt_dscp_info *info = par->matchinfo;