F1AP_LIB_FIND_IE() is used to look up elements in a list, but was
hitherto hardcoded to use "protocolIEs" as an intermediate struct. A
follow-up commit will use this macro where we don't have protocolIEs,
but "iE_Extensions". Hence, modify to make it work for that case (and
others) as well.
Robert Schmidt
3a4440a99c