Update Issue 283

 fix + non regression test case

(cherry picked from commit 041b00370bbd005a91d1632e078ed0da20b6b0a6)
fixing Firefox audio only call
Fixes issue 284
MSS-121 #Resolved Fixed

Conflicts:
	sip-servlets-core-api/src/main/java/org/mobicents/servlet/sip/core/session/MobicentsSipSession.java
	sip-servlets-impl/src/main/java/org/mobicents/servlet/sip/core/session/SipSessionImpl.java
	sip-servlets-impl/src/main/java/org/mobicents/servlet/sip/message/MobicentsSipSessionFacade.java
	sip-servlets-impl/src/main/java/org/mobicents/servlet/sip/message/SipServletRequestImpl.java