src: use namespace prefix osmo_wqueue*

Summary of changes:

s/struct write_queue/struct osmo_wqueue/g
s/write_queue_init/osmo_wqueue_init/g
s/write_queue_clear/osmo_wqueue_clear/g
s/write_queue_enqueue/osmo_wqueue_enqueue/g
s/write_queue_bfd_cb/osmo_wqueue_bfd_cb/g
diff --git a/openbsc/include/openbsc/mgcp.h b/openbsc/include/openbsc/mgcp.h
index 3d8e711..b9f8116 100644
--- a/openbsc/include/openbsc/mgcp.h
+++ b/openbsc/include/openbsc/mgcp.h
@@ -135,7 +135,7 @@
 	struct in_addr transcoder_in;
 	int transcoder_remote_base;
 
-	struct write_queue gw_fd;
+	struct osmo_wqueue gw_fd;
 
 	struct mgcp_port_range bts_ports;
 	struct mgcp_port_range net_ports;