mgcp_vty: fix config write for trunk 0

When a trunk 0 is created (which is legal) than it is impossible to
write this trunk back to the config. The reason for this that there is
still a filtering in place from the time where trunk 0 was not allowed.
This filter needs to be extended to filter only virtual trunk 0 but not
E1 trunk 0 out.

Change-Id: Iad6b577b5a711c35f98c477351fde567d8c87298
1 file changed