a_iface: OSMO_ASSERT() if we ever want to send BSSAP with invalid length

Let's add a safeguard against sending BSSAP messages with invalid length
values.  This should never happen, and we'd rather see osmo-msc assert
during the development cycle than ever releasing a version which sends
invalid messages out on the wire.

Change-Id: I94327a0d276c65b528a8c7e33dde61ed53582284
Related: OS#3805
1 file changed