FreeSWITCH-FS-6836

Merge pull request #251 in FS/freeswitch from ~DRAGOS_OANCEA/freeswitch-dragos:opus_8khz_samples_per_frame to master

* commit 'ccbef9e0c7e31c410ce08b5276c3e2e5a2f69883':
  opus@8000h : with this change there RTP timestamps will be incremented with 960 (20 ms ptime) - per RFC , and the frame size will be 160 samples.