Changes

coverity: ensure lchan->si->* bitmask sizes

osmo-bts' gsm_lchan->si bitmasks are 32 bit wide, and loops use
_MAX_SYSINFO_TYPE to iterate them. Make sure that _MAX_SYSINFO_TYPE
(from libosmocore) never surpasses 32 without us noticing the problem.

(However unlikely that is.)

Related: CID#465523
Change-Id: Ieb5d35e720e8d77336f6f912d039bab7f3b95c55