Revert "osmo-bts-trx: rx_tchf_fn(): do not treat AFS_SID_UPDATE as SUB frame"
Revert "osmo-bts-trx: rx_tchf_fn(): do not treat AFS_SID_UPDATE as SUB frame"

This reverts commit 1f9fbd881602f20f5d83b94f2332c18c19b680e0, which
was a workaround rather than a proper fix.  The root problem has
been fixed in libosmocoding [1], so ~50% BER is not the case for
AFS_SID_UPDATE frames anymore.

Related: I813081a4c0865958eee2496fe251ae17235ac842 (libosmocore.git)
Change-Id: Iebe139632daf1d1f72e39fe9d1497059f68625b9

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