i40e: don't clear suspended state until we finish resuming

When handling suspend and resume callbacks we want to make sure that (a)
we don't suspend again if we're already suspended and (b) we don't
resume again if we're already resuming. Lets make sure we test_and_set
the __I40E_SUSPENDED bit in i40e_suspend which ensures that a suspend
call when already suspended will exit early. Additionally, if
__I40E_SUSPENDED is not set when we begin resuming, exit early as well.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>