Add BTS to list at the beginning of bts_init()
Add BTS to list at the beginning of bts_init()

During init process, signals might be sent. PCU receives these signals and
requires that BTS instance is already in the list.

telenoobie/osmo-bts,osmocom/osmo-bts,geosphere/osmo-bts,telenoobie/osmo-bts,geosphere/osmo-bts,shimaore/osmo-bts,shimaore/osmo-bts,shimaore/osmo-bts,osmocom/osmo-bts,shimaore/osmo-bts,geosphere/osmo-bts,telenoobie/osmo-bts,osmocom/osmo-bts,geosphere/osmo-bts,telenoobie/osmo-bts