gsm_data_shared: drop unused *nmh from struct gsm_bts
gsm_data_shared: drop unused *nmh from struct gsm_bts

Change-Id: I57e9146cfc3274847b50caa44b09b5f06f0cf00b

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