of1.0: use tun_id instead of tun_id_

Since there is no name conflict with tun_id, no reason to use tun_id_
instead of tun_id.
This is needed for OF message conversion from/to json later.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ofproto/ofproto_parser: pylint

************* Module ryu.ofproto.ofproto_parser
W:155,4:MsgBase.__init__: __init__ method from base class 'StringifyMixin' is not called
W:186,8:MsgBase.parser: Redefining name 'msg' from outer scope (line 48)
W:240,14:ofp_attrs: Redefining name 'msg' from outer scope (line 48)
W:268,17:msg_str_attr: Redefining name 'msg' from outer scope (line 48)
E:270,20:msg_str_attr: Undefined variable 'ofp_attr'

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