native-stack: fix arp request missing under loopback connection
native-stack: fix arp request missing under loopback connection

loopback packets will throw to the NIC, but some switches may not
support send the packet back on the same link. Like back-to-back
ethernet.

So if we would like to use loopback connection, must ensure the
network env supports hairpin feature.

Signed-off-by: Haomai Wang <50290ee70f362e7f206d194c202f31d8f2037712@xsky.com>
Message-Id: <1455629943-29120-1-git-send-email-50290ee70f362e7f206d194c202f31d8f2037712@xsky.com>

syuu1228/seastar,scylladb/seastar,syuu1228/seastar,cloudius-systems/seastar,avikivity/seastar,dreamsxin/seastar,scylladb/seastar,dreamsxin/seastar,avikivity/seastar,kjniemi/seastar,scylladb/seastar,dreamsxin/seastar,syuu1228/seastar,kjniemi/seastar,avikivity/seastar,cloudius-systems/seastar,cloudius-systems/seastar,kjniemi/seastar