ofctl_v1_2/3: Convert IP fields to string with dotted decimal mask

This enables match_ip*_to_str() functions to output IP address with
dotted decimal subnet mask if the mask cannot be represented in CIDR
format.

Reported-by: Yi-Ching Lee <potatoching11@gmail.com>
Reported-by: Li-Der Chou <cld@csie.ncu.edu.tw>
Signed-off-by: Wei-Li Tang <alextwl@xinguard.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
dpset: absorb *args, **kwargs passed to __init__

dpset might be initialied implicitly like OFPHandler.
In that case, _CONTEXTS are passed to dpset. so we should ignore them.

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