gsm: Add BTS feature for Osmux

This feature is used by the BTS to signal to the BSC that it supports
using Osmux instead of RTP on the BTS<->BSC(MGW) data plane.

Related: SYS#5987
Change-Id: Ie79bfb6d0a7a8fe2842d2596b3244e7b74a0d5b6
diff --git a/include/osmocom/gsm/bts_features.h b/include/osmocom/gsm/bts_features.h
index 54f17ed..ae372d3 100644
--- a/include/osmocom/gsm/bts_features.h
+++ b/include/osmocom/gsm/bts_features.h
@@ -33,6 +33,7 @@
 	BTS_FEAT_BCCH_POWER_RED,
 	BTS_FEAT_DYN_TS_SDCCH8, /* Osmo Dynamic TS supports configured as SDCCH8 */
 	BTS_FEAT_ACCH_TEMP_OVP, /* FACCH/SACCH Temporary overpower */
+	BTS_FEAT_OSMUX, /* Osmux (Osmocom RTP muxing) support */
 	_NUM_BTS_FEAT
 };