osmo-bts-omldummy: print a brief usage statement if argc < 3
osmo-bts-omldummy: print a brief usage statement if argc < 3

Change-Id: Iff2e3c47ed12f02f75589e7bd0cccb5dab32d040

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