Revert "Fix assignment."
Revert "Fix assignment."

This reverts commit 907f856034461b6531a0e18795de2e15740e5f02.

Voiceworks/SIP.js,ronlobo/SIP.js,vconsult/JsSIP,Escaux/SIP.js,voxbone/JsSIP,AaronZhangL/JsSIP,markandrus/SIP.js,onsip/SIP.js,tqcenglish/JsSIP,josephfrazier/SIP.js,rusekr/JsSIP,CodeYellowBV/JsSIP,onsip/SIP.js,dpocock/JsSIP,DrumTechnologiesLtd/JsSIP,joseph-onsip/SIP.js