introduce `calls_sip_media_manager_get_capabilities ()` which takes
a GList of MediaCodecInfo's as input to generate a SDP message.
If using in an SDP answer we simply feed it a list of the common codecs
as gathered from the SDP offer.
by making sure the call-added signal is emitted early enough
so that all consumers (display, ringer, etc) have a chance of getting
notified when the call state changes from f.e. DIALING to DISCONNECTED
similar to how its done in 03d960ccaf
for the dummy provider.
* removed nua_callstate_authenticating as it was never hit
* move debug statement further up, because we might not reach it if no
corresponding call is found
* handle 401 and 407 the same way
note: we should record which realm we're authenticating against during
REGISTER so we can prompt the user for additional credentials when
challenged for a different realm - still happens when calling from
a sip.linphone.org account to a jmp.bwapp.bwsip.io account.
IPv6 should work, but sofia's outbound engine keep printing
errors involving the outbound engine. Working theory:
Failing ICMPv6 (pings) can make sofia think we don't have connectivity.
Note that we also don't get any answers from the SIP servers we tried so far.
