select: 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/include/osmocom/vty/telnet_interface.h b/include/osmocom/vty/telnet_interface.h
index 0c034e4..1d8055e 100644
--- a/include/osmocom/vty/telnet_interface.h
+++ b/include/osmocom/vty/telnet_interface.h
@@ -29,7 +29,7 @@
 struct telnet_connection {
 	struct llist_head entry;
 	void *priv;
-	struct bsc_fd fd;
+	struct osmo_fd fd;
 	struct vty *vty;
 	struct log_target *dbg;
 };