net: thunderbolt: Tear down connection properly on suspend

When suspending to mem or disk the Thunderbolt controller typically goes
down as well tearing down the connection automatically. However, when
suspend to idle is used this does not happen so we need to make sure the
connection is properly disconnected before it can be re-established
during resume.

Fixes: e69b6c02

 ("net: Add support for networking over Thunderbolt cable")
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>