geneve: Fix function matching VNI and tunnel ID on big-endian

On big-endian machines, functions converting between tunnel ID
and VNI use the three LSBs of tunnel ID storage to map VNI.

The comparison function eq_tun_id_and_vni(), on the other hand,
attempted to map the VNI from the three MSBs. Fix it by using
the same check implemented on LE, which maps VNI from the three
LSBs of tunnel ID.

Fixes: 2e0b26e1 ("geneve: Optimize geneve device lookup.")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: Jakub Sitnicki <jkbs@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>