rename gsm0408_gprs_rcvmsg() to gsm0408_gprs_rcvmsg_gb()

This is the entry point for GMM from Gb.  We will create a new one
for Iu, so let's be explicit rather than implicit.

Change-Id: I93c074bf99db041117c0dc03dc8255879845a875
diff --git a/openbsc/tests/sgsn/sgsn_test.c b/openbsc/tests/sgsn/sgsn_test.c
index 3fb359b..48f013d 100644
--- a/openbsc/tests/sgsn/sgsn_test.c
+++ b/openbsc/tests/sgsn/sgsn_test.c
@@ -196,7 +196,7 @@
 	msg = create_msg(data, data_len);
 	msgb_tlli(msg) = tlli;
 	bssgp_create_cell_id(msgb_bcid(msg), bssgp_raid, 0);
-	gsm0408_gprs_rcvmsg(msg, llme);
+	gsm0408_gprs_rcvmsg_gb(msg, llme);
 	msgb_free(msg);
 }