MS Power Control Loop: Disable threshold comparison on {LOWER,UPPER}_CMP_N=0
MS Power Control Loop: Disable threshold comparison on {LOWER,UPPER}_CMP_N=0

This way we provide an effective way to disable C/I based decision
taking in the MS Power Control Loop. With this set up, MS Power Level is
decided only based on RxLev. This allows for working setup in following
scenarios:
* BTS L1 not passing proper C/I values to upper layers (eg. TRXDv0).
* User not willing to spend time configuring proper C/I levels for each
  channel type.

Related: SYS#4917
Change-Id: Ibd10eb96a5d072d5c19f7449a8b11e64aad1cd4c

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