Two calls screen is not displayed on multiple SIP calls

When accepting the 2nd incoming SIP call, the 1st SIP call is set to
Hold call by calling SipPhone#switchHoldingAndActive().
However, Hold call is returned to Active call afterwards because
switchHoldingAndActive() is called by the TelephonyFWK side again.
Therefore, two calls screen is not displayed because Hold call does
not exist.

Change-Id: I623a67c2493fe7c4bcd8b36f3b13ede31f36b820
1 file changed