soc: qcom: ipc_router_glink_xprt: Reset the link state correctly

The G-Link channel handle is not reset after the channel is closed.
This causes the link to be not re-initialized after it is closed.

Reset the G-Link channel handle after closing it as part of handling
subsystem restart. Handle the disconnect event only once.

CRs-Fixed: 848049
Change-Id: Ib3449cbca7c1d11a6f4020099bea4a1488ae1f2f
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>