[BSC] fix off-by-one error in computing l2 pseudo-length in IMM ASS

@fingerprint:
This caused Motorole EZX phones (Neptune LTE chipset) to discard
all immediate assigns and thus be unable to perform location updating.
1 file changed
tree: 57d9bb07ba25d25d5c92173fdf3505aa99ca23f6
  1. hlrsync/
  2. linux-kernel/
  3. openbsc/
  4. wireshark/