To display NAT-related settings.
UDP Keep Alive message: If enabled, IP phone will send
UDP keep-alive message periodically to router to keep NAT
port alive.
UDP Alive Msg Interval: Keepalive message interval.
Rport: Remote Port, if enabled, it will add Remote Port into
outgoing SIP message for designated account.
One can customize User Agent field in the SIP message; if
user agent is set to specific value, user can see the
information from PCAP. If user agent is not set by default,
users can see the company name, model number and
firmware version from PCAP.