Transceiver52M: Match handover and slot mask flags with TransceiverRAD1

The following flags affect GPRS performance.

Add flags for HANDOVER/NOHANDOVER commands, which force RACH burst
processing on selected slots. Also turn on the previously disabled
filler table slot mask (i.e. 'Magic flag').

These changes match Transceiver52M with TransceiverRAD1 command handling
that took place in commit

5289a229d9f92b5e18798671c3dd457a3ee66bc4 'sync of openbts'

Signed-off-by: Thomas Tsou <tom@tsou.cc>