Map ImsReasonInfo.CODE_SIP_USER_REJECTED(SIP 603 DECLINE) as DisconnectCause.NORMAL

Network doesn't treat SIP 603 DECLINE as error condition
This can be observed from some carrier requirements like VZW
VZ_REQ_IMS_22961 or Softbank OTR-Voice-032026
So we should not treat it as server error.

Bug: b/119804523
Test: Build pass
Change-Id: I98d088120096a5686f788d85ecbc205e65475b15