NethVoice: don't add proxy on trunk configuration named Identity0

[andrea-marchionni]

To handle credentials with usernames in the format sip:XXXXXX@XXXXXX, it is not possible to configure the trunk name using the term "custom."
Therefore, it is necessary to ensure that the proxy is not repopulated, even for the identity field.

[Amygos]

Testing release nethesis/ns8-nethvoice 1.1.4-testing.6