Ensure IMS conference participants have number presentation set.

When anonymous participants are added in an IMS conference call, the
number presentation was not set.  Since the address is null it meant
they would be defaulted to UNKNOWN.

Fixed to ensure the number presentation is set as well.

Test: Manual
Bug: 62475520
Change-Id: I98fbbd0c0a04ef34e9b26d092d6b45fa226f9d7b