i40iw: Use correct address in dst_neigh_lookup for IPv6

Use of incorrect structure address for IPv6 neighbor lookup
causes connections to IPv6 addresses to fail. Fix this by
using correct address in call to dst_neigh_lookup.

Fixes: f27b4746 ("i40iw: add connection management code")
Signed-off-by: Mustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>