DNS NAPTR-SRV query is not triggered if SipStack is started

[MassimoMessore]

Configuration:

• P-CSCF address set in the Network settings
• P-CSCF address need to be translated via NAPTR-SRV query

Issue: When NgnSipService::register() is called:

• If the Sip stack is not started yet, the proxy address is correctly solved via NAPTR-SRV query
• If the Sip stack is already started, the proxy address cannot be translated because the DNS query used is of type A.

Workaround: In Doubango -> tsip.c file -> tsip_stack_start() function, move the piece of code that performs the NAPTR-SRV checks before return 0 if the stack is already started.