libmsc/osmo_msc.c: move connection ref-counting code to 'ran_conn.c'

The connection ref-counting implementation is specific to RAN
connections, and is not applicable for anything else. Moreover,
the API of this code is declared in 'ran_conn.h', so let's
move the code to a more logical place.

Change-Id: I593675d9bf56eaef12afdaf596ee1337b9a44259
2 files changed