Change the behaviour of DTMF sending

When both "use_rfc2833" and "use_info" are enabled on a Core, use SIP INFO only as fallback for when a media does not support out-of-band DTMF events

(cherry picked from commit 680d0928)

Children:

• liblinphone!2476 (merged)
• mediastreamer2!802 (merged)

https://bugs.linphone.org/view.php?id=11573