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/include/openbsc/rtp_proxy.h b/openbsc/include/openbsc/rtp_proxy.h
index 8ad3636..3b208c3 100644
--- a/openbsc/include/openbsc/rtp_proxy.h
+++ b/openbsc/include/openbsc/rtp_proxy.h
@@ -48,7 +48,7 @@
 	struct sockaddr_in sin_local;
 	struct sockaddr_in sin_remote;
 
-	struct bsc_fd bfd;
+	struct osmo_fd bfd;
 	/* linked list of to-be-transmitted msgb's */
 	struct llist_head tx_queue;
 };