[reSIProcate] OnGlare(or 491 message) handler

["Wenwei Xu" <wxu@xxxxxxxxxxxxx>]

I introduced an onGlare() handler into the InviteSessionHandler class and
wanted to place the function call in the following function block. So when a
UA gets a 491 message, it can have some sort of control on its own. Please
comment.

void
InviteSession::start491Timer()
{
   int seq = mLastSessionModification.header(h_CSeq).sequence();
   int timer = Random::getRandom() % 4000;
   mDum.addTimerMs(DumTimeout::Glare, timer, getBaseHandle(), seq);

   //add onGlare handler here
   InviteSessionHandler* handler = mDum.mInviteSessionHandler;
   handler->onGlare(getSessionHandle());
}