select: Rename BSC_FD_* constants to OSMO_FD_*

The naming of these constants dates back to when the code was private
within OpenBSC.  Everything else was renamed (bsc_fd -> osmo_fd) at
the time, but somehow the BSC_FD_* defines have been missed at the
time.

Keep compatibility #defines around, but allow us to migrate the
applications to a less confusing naming meanwhile.

Change-Id: Ifae33ed61a7cf0ae54ad487399e7dd2489986436
diff --git a/src/gb/gprs_ns.c b/src/gb/gprs_ns.c
index 8c3b0fa..c7ff78e 100644
--- a/src/gb/gprs_ns.c
+++ b/src/gb/gprs_ns.c
@@ -2006,9 +2006,9 @@
 {
 	int rc = 0;
 
-	if (what & BSC_FD_READ)
+	if (what & OSMO_FD_READ)
 		rc = handle_nsip_read(bfd);
-	if (what & BSC_FD_WRITE)
+	if (what & OSMO_FD_WRITE)
 		rc = handle_nsip_write(bfd);
 
 	return rc;