PCUIF: rename tlli to msg_id

To confirm downlink IMMEDIATE ASSIGNMENT messages, we use the TLLI as an
identifier and the related record member is also called "tlli".
Unfortunately this is misleading since the message identifier does not
necessarly have to be a TLLI. It is just an implementation detail that
osmo-pcu uses the TLLI as a message identifier.

To make that clear, lets rename the tlli member (and variable and
parameter names where it is passed on) to "msg_id".

(Since this change only renames variables and struct members it will not
break compatibility with other programs that use the PCUIF)

Related: OS#5927
Depends: osmo-pcu.git I4a25039dfe329e68879bc68936e49c4b190625e6
Change-Id: I1db29d5b1920e351c452b798c3260654c2cbe0cb
4 files changed