ipv4: Fix raw socket lookup for local traffic

commit 19e4e768 upstream.

inet_iif should be used for the raw socket lookup. inet_iif considers
rt_iif which handles the case of local traffic.

As it stands, ping to a local address with the '-I <dev>' option fails
ever since ping was changed to use SO_BINDTODEVICE instead of
cmsg + IP_PKTINFO.

IPv6 works fine.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>