usb: wwan: Fix list corruption during port re-open

The Rx URB processing working is not cancelled during port close. If
the port is immediately opened, it may run in parallel with Rx URB
processing work and it leads to the list corruption. Cancel the Rx URB
processing work while closing the port. Also don't schedule this work from
Rx complete callback if port is closed.

CRs-Fixed: 554519
Change-Id: I48919770b69136e62b3f54586875868cc06b8d0b
Signed-off-by: Chandana Kishori Chiluveru <cchilu@codeaurora.org>