igb: fix NULL derefs due to skipped SR-IOV enabling

The combined effect of commits 6423fc3416 ("igb: do not re-init SR-IOV
during probe") and ceee3450b3 ("igb: make sure SR-IOV init uses the
right number of queues") causes VFs no longer getting set up, leading
to NULL pointer dereferences due to the adapter's ->vf_data being NULL
while ->vfs_allocated_count is non-zero. The first commit not only
neglected the side effect of igb_sriov_reinit() that the second commit
tried to account for, but also that of setting IGB_FLAG_HAS_MSIX,
without which igb_enable_sriov() is effectively a no-op. Calling
igb_{,re}set_interrupt_capability() as done here seems to address this,
but I'm not sure whether this is better than sinply reverting the other
two commits.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -2858,6 +2858,13 @@ static void igb_probe_vfs(struct igb_adapter *adapter)
 	if ((hw->mac.type == e1000_i210) || (hw->mac.type == e1000_i211))
 		return;
 
+	/* Of the below we really only want the effect of getting
+	 * IGB_FLAG_HAS_MSIX set (if available), without which
+	 * igb_enable_sriov() has no effect.
+	 */
+	igb_set_interrupt_capability(adapter, true);
+	igb_reset_interrupt_capability(adapter);
+
 	pci_sriov_set_totalvfs(pdev, 7);
 	igb_enable_sriov(pdev, max_vfs);