The 'UP' status indicates a gateway is online as determined by
registration and/or SIP OPTIONS pinging.

The time the gateway has been in the 'UP' status is recorded,
and can be monitored using 'sofia status' and 'sofia xmlstatus'.

This can be used to detect and graph when there are outages.

ref: FS-6772
Reviewed-by: Travis Cross <tc@traviscross.com>