Martin Tomec

There was functionality in chan_sip to get REFER headers, with GET_TRANSFERRER_DATA variable. This commit implements the same functionality in pjsip, to ease transfer from chan_sip to pjsip. Fixes: #579 UserNote:...

### Improvement Description Issue to track patch submission. There is functionality in chan_sip to get REFER headers, with GET_TRANSFERRER_DATA variable. This is not implemented in pjsip, but demanded here: https://community.asterisk.org/t/reading-refer-header/91876...