chan_sip: Emit a second ringing event to ensure channel is found.

chan_sip: Emit a second ringing event to ensure channel is found.

When constructing a dialog-info+xml NOTIFY message a ringing channel
is found if the state is ringing and further information is placed into
the message. Due to the migration to the Stasis message bus this did
not always work as expected.

This change raises a second ringing event in such a way to guarantee
that the event is received by chan_sip and another lookup is done to
find the ringing channel.

ASTERISK-24488

Change-Id: I547a458fc59721c918cb48be060cbfc3c88bcf9c