packet lib: implement basic part of BGP-4

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
unit test for lib.packet.bgp

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
doc: hook up lib.packet.bgp

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
streaming parser base class

will be used for BGP-4.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
implement BGP-4 streaming parser

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
doc: hook up streaming parser docs

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