i40evf: Fix double locking the same resource

Removes the locking of adapter->mac_vlan_list_lock resource in
i40evf_add_filter(). The locking part is moved above i40evf_add_filter().
i40evf_add_filter(), called by i40evf_addr_sync(), was trying to lock the
resource again and double locking generated a kernel panic after bringing
an interface up.

Fixes: 8946b563 ("i40evf: use __dev_[um]c_sync routines in
       .set_rx_mode")
Signed-off-by: Paweł Jabłoński <pawel.jablonski@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>