Changes

hnbgw: Fix wrong map object retrieved from hashtable

If several map objects (mapping between RUA and SCCP transports for a
given Iu connection) ended up in the same hashtable bucket, then the
first one was always returned by map_from_conn_id().

As a result, when such collisions happened (e.g. when a big number of
connections were inserted) a user could see a Iu message coming from SCCP
connection "A" end up being forwarded to an unrelated RUA connection
"B".

Related: SYS#6602
Change-Id: I107f461bf5bcb92262422c893b23d190659f6f72