Add experimental 'pre-ts-ack' to the 'immediate-assignment' options:
send the IMM ASS even before a dynamic timeslot is switched. This
possibly saves an Abis roundtrip, but may be racy.
When pre-ts-ack is chosen, already do the IMM ASS before the dyn TS
pchan switch is ACKed.
In Immediate Assignment, in case the dyn TS is not ready yet, get the
pchan kind from lchan->type, which already reflects the target type, and
not from ts->pchan_is, which still reflects the previous pchan type.
Related test is in I2ae28cd92910d4bc341a88571599347a64a18fe5
Related: SYS#5559
Change-Id: I19e6a3d614aa5ae24d64eed96caf53e6f0e8bb74
c746509d3c