osmo-bts-trx: indicate BTS_FEAT_EGPRS support to BSC
osmo-bts-trx: indicate BTS_FEAT_EGPRS support to BSC

EGPRS support, in particular MCS channel coding, was introduced
to osmo-bts-trx years ago, but we still report that it's not
supported. Let's stop confusing BSC, and set this feature too.

Change-Id: Iaf92764d266e12efd2350967deffae50fbbb3b9e

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts