sysmobts: normalize frame number in measurement indication
sysmobts: normalize frame number in measurement indication

The higher layers relay on a normalized version of frame number
in order to detect the end of a measurement period.

The frame number on which the measurement reports are sent may
depend on the phy, so we need to normalize the frame number
before we report it to the higher layers.

Change-Id: I90bd01479e41f04a6b0aefe3845d071e3148d0c6

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