Changed SgNB UE X2AP ID to be an optional IE in SGNB ADDITION REQUEST REJECT
to be compatible with 3GPP 36.423 standard. API backward incompatible change.
Signed-off-by: Timo Tietavainen <timo.tietavainen@nokia.com>
Change-Id: I5c42fdd22eec4a1b4632c1acd12b8f6b7e183396