bgp: bug fix of handling nexthop for eBGP peering

RyuBGP doesn't work properly becase of handling wrong nexthop address.
Therefore, in spite of receiving BGP UPDATE Message in the peering router,
the router fails to learn a new route entry from RyuBGP in BGP table.
(Memo: this issue has not occurred in Vpnv4/mpBGP environment.)

(1) register route entry as prefix_add(prefix='x,x,x,x', next_hop='y.y.y.y')

                 static               eBGP
    ------- R1 ------------ RyuBGP ---------> Router
    x.x.x.x   y.y.y.y            z.z.z.z       => Drop UPDATE(Nexthop: y.y.y.y)

(2) receiving BGP UPDATE Message from iBGP session

                 iBGP                 eBGP
    ------- R1 -----------> RyuBGP ---------> Router
    x.x.x.x   y.y.y.y            z.z.z.z       => Drop UPDATE(Nexthop: y.y.y.y)

Signed-off-by: Toshiki Tsuboi <t.tsubo2000@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ofctl_v1_/2/3: Modify match_to_str() to use new match field parser

Signed-off-by: Minoru TAKAHASHI <takahashi.minoru7@gmail.com>
Signed-off-by: IWASE Yusuke <iwase.yusuke0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ofctl_v1_/2/3: Modify to_match() to use new match api

Signed-off-by: Minoru TAKAHASHI <takahashi.minoru7@gmail.com>
Signed-off-by: IWASE Yusuke <iwase.yusuke0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
test_ofctl: Modify to use new match api and field parser

Signed-off-by: Minoru TAKAHASHI <takahashi.minoru7@gmail.com>
Signed-off-by: IWASE Yusuke <iwase.yusuke0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Workaround of os.path.samefile

os.path.samrfile not implemented on Windows. Adding alternative using
os.stat

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>