Use OSMO_FD_* instead of deprecated BSC_FD_*

New define is available since libosmocore 1.1.0, and we already require
1.2.0, so no need to update dependenices.
Let's change it to avoid people re-using old BSC_FD_* symbols when
copy-pasting somewhere else.

Change-Id: Iaebd049e383b02204a12f39cc6c932a53d25fd72
diff --git a/src/gtphub/gtphub.c b/src/gtphub/gtphub.c
index ca5857b..7b355bf 100644
--- a/src/gtphub/gtphub.c
+++ b/src/gtphub/gtphub.c
@@ -853,7 +853,7 @@
 		return -1;
 	}
 
-	ofd->when = BSC_FD_READ;
+	ofd->when = OSMO_FD_READ;
 	ofd->cb = cb;
 	ofd->data = data;
 	ofd->priv_nr = ofd_id;
@@ -1948,7 +1948,7 @@
 	LOG(LOGL_DEBUG, "=== reading from SGSN (%s)\n",
 	    gtphub_plane_idx_names[plane_idx]);
 
-	if (!(what & BSC_FD_READ))
+	if (!(what & OSMO_FD_READ))
 		return 0;
 
 	struct gtphub *hub = from_sgsns_ofd->data;
@@ -1979,7 +1979,7 @@
 	OSMO_ASSERT(plane_idx < GTPH_PLANE_N);
 	LOG(LOGL_DEBUG, "=== reading from GGSN (%s)\n",
 	    gtphub_plane_idx_names[plane_idx]);
-	if (!(what & BSC_FD_READ))
+	if (!(what & OSMO_FD_READ))
 		return 0;
 
 	struct gtphub *hub = from_ggsns_ofd->data;