USB: android: Fix rmnet_gport_setup error path handling on sigkill

rmnet_gport_setup might fail if userspace killed adbd while
usb_add_config was executed in its context. This results in
alloc_workqueue failure followed by rmnet_gport_setup bailing
out. Next time when adbd is started, gport_setup doesnt happen
(due to rmnet_initialized) and rmnet bind_config fails. Fix
this by setting rmnet_initialized only when rmnet_gport_setup
is successful and also perform cleanup when gport_setup fails.

CRs-Fixed: 1021758
Change-Id: Ia0df36f734ba2e2ad54dec6e93d80593c4813447
Signed-off-by: Arumuga Durai A <cadurai@codeaurora.org>