If a switch is invoked using chan_iax2, deadlock can result
because the PBX core is autoservicing the channel while chan_iax2
also then attempts to service it while waiting for the result
of the switch. This removes servicing of the channel to prevent
any conflicts.
ASTERISK-30064 #close
Change-Id: Ie92f206d32f9a36924af734ddde652b21106af22