nat: Attempt to follow the MODULE_METHOD pattern for methods

Rename methods to be like bsc_ussd_ACTION.
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat.c b/openbsc/src/osmo-bsc_nat/bsc_nat.c
index 1eac983..2254a8d 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat.c
@@ -1081,7 +1081,7 @@
 					}
 
 					/* hand data to a side channel */
-					if (bsc_check_ussd(con, parsed, msg) == 1) 
+					if (bsc_ussd_check(con, parsed, msg) == 1) 
 						con->con_local = NAT_CON_END_USSD;
 
 					/*
@@ -1093,7 +1093,7 @@
 					talloc_free(parsed);
 					parsed = NULL;
 				} else if (con->con_local == NAT_CON_END_USSD) {
-					bsc_check_ussd(con, parsed, msg);
+					bsc_ussd_check(con, parsed, msg);
 				}
 
 				con_bsc = con->bsc;
@@ -1595,7 +1595,7 @@
 }
 
 /* Close all connections handed out to the USSD module */
-int bsc_close_ussd_connections(struct bsc_nat *nat)
+int bsc_ussd_close_connections(struct bsc_nat *nat)
 {
 	struct nat_sccp_connection *con;
 	llist_for_each_entry(con, &nat->sccp_connections, list_entry) {
diff --git a/openbsc/src/osmo-bsc_nat/bsc_ussd.c b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
index d422f9e..8da8181 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_ussd.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
@@ -58,7 +58,7 @@
 static void bsc_nat_ussd_destroy(struct bsc_nat_ussd_con *con)
 {
 	if (con->nat->ussd_con == con) {
-		bsc_close_ussd_connections(con->nat);
+		bsc_ussd_close_connections(con->nat);
 		con->nat->ussd_con = NULL;
 	}
 
@@ -360,7 +360,7 @@
 	return 0;
 }
 
-int bsc_check_ussd(struct nat_sccp_connection *con, struct bsc_nat_parsed *parsed,
+int bsc_ussd_check(struct nat_sccp_connection *con, struct bsc_nat_parsed *parsed,
 		   struct msgb *msg)
 {
 	uint32_t len;