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/tests/timer/timer_test.c b/tests/timer/timer_test.c
index 69bcad9..240bc48 100644
--- a/tests/timer/timer_test.c
+++ b/tests/timer/timer_test.c
@@ -69,7 +69,7 @@
 
 #ifdef HAVE_SYS_SELECT_H
     while (1) {
-        bsc_select_main(0);
+        osmo_select_main(0);
     }
 #else
     printf("Select not supported on this platform!\n");