ixgbe: release lock for the duration of ixgbe_suspend_close()

ixgbe: release lock for the duration of ixgbe_suspend_close()

Currently, during device_shutdown() ixgbe holds rtnl_lock for the duration
of lengthy ixgbe_close_suspend(). On machines with multiple ixgbe cards
this lock prevents scaling if device_shutdown() function is multi-threaded.

It is not necessary to hold this lock during ixgbe_close_suspend()
as it is not held when ixgbe_close() is called also during shutdown but for
kexec case.

Signed-off-by: Pavel Tatashin <[email protected]>
Tested-by: Andrew Bowers <[email protected]>
Signed-off-by: Jeff Kirsher <[email protected]>