gbproxy: Rename identifiers related to IMSI matching

This patch renames gbproxy_check_tlli() to
gbproxy_imsi_matches() and struct tlli_info's
enable_patching to imsi_matches.

It's meant to be more obvious and consistent this way.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/gprs/gb_proxy.c b/openbsc/src/gprs/gb_proxy.c
index 8b5a672..886d3c3 100644
--- a/openbsc/src/gprs/gb_proxy.c
+++ b/openbsc/src/gprs/gb_proxy.c
@@ -574,7 +574,7 @@
 	if (tlli_info && cfg->route_to_sgsn2) {
 		if (cfg->acquire_imsi && tlli_info->imsi_len == 0)
 			sgsn_nsei = 0xffff;
-		else if (gbproxy_check_tlli(peer, tlli_info))
+		else if (gbproxy_imsi_matches(peer, tlli_info))
 			sgsn_nsei = cfg->nsip_sgsn2_nsei;
 	}