Changes

rsl: parse OSMO_IE_OSMO_OSMUX_CID correctly

This IE has TLV format, even though the only valid form is a single
value octet.  To guard against pathological input with L=0 in this IE,
we have to check the length explicitly with TLVP_PRES_LEN before
accepting TLVP_VAL as if it was TV.

Change-Id: I15fa75b6c30d7fa0bf50424d25fc47a088dada0a