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-nitb/bsc_hack.c b/openbsc/src/osmo-nitb/bsc_hack.c
index 8fec368..261c426 100644
--- a/openbsc/src/osmo-nitb/bsc_hack.c
+++ b/openbsc/src/osmo-nitb/bsc_hack.c
@@ -307,6 +307,6 @@
 
 	while (1) {
 		log_reset_context();
-		bsc_select_main(0);
+		osmo_select_main(0);
 	}
 }