mgcp_network: Unregister osmo_fd before closing fd

(cherry picked from commit 6c303664f5154f22a881f450a7d6d3bbae0ccacc)

Change-Id: Id03011a11be17e9c0a53b01444754dd633232d2e
diff --git a/src/libosmo-mgcp/mgcp_network.c b/src/libosmo-mgcp/mgcp_network.c
index d6028a2..af9ae99 100644
--- a/src/libosmo-mgcp/mgcp_network.c
+++ b/src/libosmo-mgcp/mgcp_network.c
@@ -1676,14 +1676,14 @@
 void mgcp_free_rtp_port(struct mgcp_rtp_end *end)
 {
 	if (end->rtp.fd != -1) {
+		osmo_fd_unregister(&end->rtp);
 		close(end->rtp.fd);
 		end->rtp.fd = -1;
-		osmo_fd_unregister(&end->rtp);
 	}
 
 	if (end->rtcp.fd != -1) {
+		osmo_fd_unregister(&end->rtcp);
 		close(end->rtcp.fd);
 		end->rtcp.fd = -1;
-		osmo_fd_unregister(&end->rtcp);
 	}
 }