LMSDevice: Set low-pass filters to smallest possible option
LMSDevice: Set low-pass filters to smallest possible option

Rx 1.4 MHz, Tx 5MHz.  Both massively too wide for GSM, but there's
no smaller band-width available.

Change-Id: I9723c9a2ea77f65bfa9d796d7c44adc2417e89cf

osmocom/osmo-trx,ttsou/osmo-trx,ttsou/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx,ttsou/osmo-trx,osmocom/osmo-trx,ttsou/osmo-trx