auth: Release the security operation after we sent out a message

The release might release the lchan we want to send the response
on. Reorder the code to first send the message and then give up
the security operation which might release the lchan.
diff --git a/openbsc/src/gsm_04_08.c b/openbsc/src/gsm_04_08.c
index 92da6cc..d6d9b98 100644
--- a/openbsc/src/gsm_04_08.c
+++ b/openbsc/src/gsm_04_08.c
@@ -927,6 +927,7 @@
 
 	/* Validate SRES */
 	if (memcmp(conn->sec_operation->atuple.sres, ar->sres,4)) {
+		int rc;
 		gsm_cbfn *cb = conn->sec_operation->cb;
 
 		DEBUGPC(DMM, "Invalid (expected %s)\n",
@@ -936,8 +937,9 @@
 			cb(GSM_HOOK_RR_SECURITY, GSM_SECURITY_AUTH_FAILED,
 			   NULL, conn, conn->sec_operation->cb_data);
 
+		rc = gsm48_tx_mm_auth_rej(conn);
 		release_security_operation(conn);
-		return gsm48_tx_mm_auth_rej(conn);
+		return rc;
 	}
 
 	DEBUGPC(DMM, "OK\n");