octphy: remap frame number in MEAS_IND
octphy: remap frame number in MEAS_IND

The octasic phy stamps the SACCH channel that carries the
measurmenet indication with the frame number of the last
SACCH that falls within the measurement period.

The higher layers expect the frame number to be aligned
to the SACCH channel after, which marks also the beginning
of the next measurement period.

Make the octphy code compatible to the higher layers by
remapping the measurement indication frame number.

Change-Id: I8ecb27c018bf4ad5151878a6ad34026fd0f801a1

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