bts-trx: Instruct user to set manually nominal-tx-power if NOMTXPOWER not supported
bts-trx: Instruct user to set manually nominal-tx-power if NOMTXPOWER not supported

Using the VTY command will force that value and prevent osmo-bts-trx to
use/send NOMTXPOWER cmd over TRXC.

Change-Id: I496753bc74767a7e18b831768d9d422a738192b7

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