Fix a corner case issue when daemon panics

There is an extreme corner case where when the daemon
panics at the same time as a container is stopping
and cleaning up the sandbox and the sandbox may have been
left with an inconsistent state. This libnetwork vendoring
fixes that case.

Vendoring in libnetwork @ 5305ea570b85d61dd0fd261cd7e1680da1884678

Signed-off-by: Jana Radhakrishnan <mrjana@docker.com>