cdr.c: Set tenantid from party_a->base instead of chan->base.

cdr.c: Set tenantid from party_a->base instead of chan->base.

The CDR tenantid was being set in cdr_object_alloc from the channel->base
snapshot.  Since this happens at channel creation before the dialplan is even
reached, calls to `CHANNEL(tenantid)=<something>` in the dialplan were being
ignored.  Instead we now take tenantid from party_a when
cdr_object_create_public_records() is called which is after the call has
ended and all channel snapshots rebuilt.  This is exactly how accountcode
and amaflags, which can also be set in tha dialplpan, are handled.

Resolves: #1259