gprs_gmm: Fix missing Security Command for 3G when attaching

Introduce a new FSM step in GMM Attach to send the
Security Command to the RNC after completing the
Authentication.

Fixes: f7198d7dbb84 ("gprs_gmm: introduce a GMM Attach Request FSM")
Change-Id: I1e12b0a32e58c6f78dba7b548f7d7016567229db
diff --git a/src/gprs/gprs_gmm.c b/src/gprs/gprs_gmm.c
index a86fe2b..a0221ea 100644
--- a/src/gprs/gprs_gmm.c
+++ b/src/gprs/gprs_gmm.c
@@ -205,7 +205,7 @@
 		REQUIRE_MM
 		/* Continue authentication here */
 		mm->iu.ue_ctx->integrity_active = 1;
-		rc = gsm48_gmm_authorize(mm);
+		osmo_fsm_inst_dispatch(mm->gmm_att_req.fsm, E_IU_SECURITY_CMD_COMPLETE, NULL);
 		break;
 	default:
 		LOGP(DRANAP, LOGL_NOTICE, "Unknown event received: %i\n", type);