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/osmo-bsc_mgcp/mgcp_main.c b/openbsc/src/osmo-bsc_mgcp/mgcp_main.c
index 2077929..8cb90c5 100644
--- a/openbsc/src/osmo-bsc_mgcp/mgcp_main.c
+++ b/openbsc/src/osmo-bsc_mgcp/mgcp_main.c
@@ -135,7 +135,7 @@
 	return 0;
 }
 
-static int read_call_agent(struct bsc_fd *fd, unsigned int what)
+static int read_call_agent(struct osmo_fd *fd, unsigned int what)
 {
 	struct sockaddr_in addr;
 	socklen_t slen = sizeof(addr);
@@ -254,7 +254,7 @@
 		}
 
 
-		if (bsc_register_fd(&cfg->gw_fd.bfd) != 0) {
+		if (osmo_fd_register(&cfg->gw_fd.bfd) != 0) {
 			LOGP(DMGCP, LOGL_FATAL, "Failed to register the fd\n");
 			return -1;
 		}
@@ -275,7 +275,7 @@
 
 	/* main loop */
 	while (1) {
-		bsc_select_main(0);
+		osmo_select_main(0);
 	}