iwlwifi: mvm: fix d3_test with unified D0/D3 images

When a unified D0/D3 image is used, we don't restart the FW in the
D0->D3->D0 transitions.  Therefore, the d3_test functionality should
not call ieee8021_restart_hw() when the resuming either.

Fixes: commit 23ae6128 ("iwlwifi: mvm: Do not switch to D3 image on suspend")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>