[VAMOS] l1sap_chan_act(): handle Osmocom specific TSC IE
[VAMOS] l1sap_chan_act(): handle Osmocom specific TSC IE

This is an Osmocom specific RSL IE that, if present, takes
precedence over the values indicated via the A-bis/OML.

Change-Id: I717e5b2a6ca5b4faeaab9cae4bb971907945871b
Related: SYS#4895, OS#4941

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