[mod_sofia] Fixing deadlock in issue #2290

[mishehu]

I cannot certify that on SWITCH_MESSAGE_INDICATE_TRANSCODING_NECESSARY that we should be following this code path, but it does not look like there's anything that gets changed when we enter sofia_receive_message() in this case. Thus there's no sense in locking tech_pvt->sofia_mutex , thus avoiding the deadlock described in issue #2290.

[signalwire-ci[bot]]

Unit-tests failed: https://public-artifacts.signalwire.cloud/drone/signalwire/freeswitch/1685/artifacts.html