IPoIB: Fix ipoib_neigh hashing to use the correct daddr octets

The hash function introduced in commit b63b70d8 ("IPoIB: Use a
private hash table for path lookup in xmit path") was designd to use
the 3 octets of the IPoIB HW address that holds the remote QPN.
However, this currently isn't the case on little-endian machines,
because the the code there uses the flags part (octet[0]) and not the
last octet of the QPN (octet[3]).  Fix this.

The fix caused a checkpatch warning on line over 80 characters, to
solve that changed the name of the temp variable that holds the daddr.

Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>