msm: ipa3: Fix to start/stop gsi channel USB pipe connected

Observing the race condition without USB pipe connected
try to start/stop channel during SSR. Added changes to
start/stop channel only if when USB connected.

Change-Id: I06756481c93395885a527b5d01b75719ccf9405e
Signed-off-by: Ashok Vuyyuru <avuyyuru@codeaurora.org>