src: use namespace prefix osmo_fd* and osmo_select*

Summary of changes:

s/struct bsc_fd/struct osmo_fd/g
s/bsc_register_fd/osmo_fd_register/g
s/bsc_unregister_fd/osmo_fd_unregister/g
s/bsc_select_main/osmo_select_main/g
diff --git a/openbsc/src/libtrau/rtp_proxy.c b/openbsc/src/libtrau/rtp_proxy.c
index 04e224c..86d5624 100644
--- a/openbsc/src/libtrau/rtp_proxy.c
+++ b/openbsc/src/libtrau/rtp_proxy.c
@@ -482,7 +482,7 @@
 
 
 /* callback for the select.c:bfd_* layer */
-static int rtp_bfd_cb(struct bsc_fd *bfd, unsigned int flags)
+static int rtp_bfd_cb(struct osmo_fd *bfd, unsigned int flags)
 {
 	struct rtp_socket *rs = bfd->data;
 	struct rtp_sub_socket *rss;
@@ -536,7 +536,7 @@
 		goto out_free;
 
 	init_rss(&rs->rtp, rs, rc, RTP_PRIV_RTP);
-	rc = bsc_register_fd(&rs->rtp.bfd);
+	rc = osmo_fd_register(&rs->rtp.bfd);
 	if (rc < 0)
 		goto out_rtp_socket;
 
@@ -545,7 +545,7 @@
 		goto out_rtp_bfd;
 
 	init_rss(&rs->rtcp, rs, rc, RTP_PRIV_RTCP);
-	rc = bsc_register_fd(&rs->rtcp.bfd);
+	rc = osmo_fd_register(&rs->rtcp.bfd);
 	if (rc < 0)
 		goto out_rtcp_socket;
 
@@ -558,11 +558,11 @@
 	return rs;
 
 out_rtcp_bfd:
-	bsc_unregister_fd(&rs->rtcp.bfd);
+	osmo_fd_unregister(&rs->rtcp.bfd);
 out_rtcp_socket:
 	close(rs->rtcp.bfd.fd);
 out_rtp_bfd:
-	bsc_unregister_fd(&rs->rtp.bfd);
+	osmo_fd_unregister(&rs->rtp.bfd);
 out_rtp_socket:
 	close(rs->rtp.bfd.fd);
 out_free:
@@ -713,11 +713,11 @@
 	    rs->proxy.other_sock)
 		rs->proxy.other_sock->proxy.other_sock = NULL;
 
-	bsc_unregister_fd(&rs->rtp.bfd);
+	osmo_fd_unregister(&rs->rtp.bfd);
 	close(rs->rtp.bfd.fd);
 	free_tx_queue(&rs->rtp);
 
-	bsc_unregister_fd(&rs->rtcp.bfd);
+	osmo_fd_unregister(&rs->rtcp.bfd);
 	close(rs->rtcp.bfd.fd);
 	free_tx_queue(&rs->rtcp);