Add IPAddr#wildcard_mask

[taketo1113]

Added to get an address of wildcard mask which is like a reverse subnet mask.
It uses to configure a network device for ACL or OSPF.

Related links

• Wildcard Mask
  • https://en.wikipedia.org/wiki/Wildcard_mask
  • https://www.ciscopress.com/articles/article.asp?p=3089353&seqNum=5

[sorah]

Hi,

I'd like to take a look at this PR (sorry for being too late!)

I believe this is sourced from https://github.com/interop-tokyo-shownet/ipaddr-ext and I noticed the difference in license. Since ipaddr-ext has only 1 author (you), it'd be easy to merge if you relicense ipaddr-ext to match this gem (Dual license of Ruby/BSD-2-Clause) first.

I'm also interested in upstreaming of other extensions in ipaddr-ext to ruby/ipaddr if you'd like…!

[taketo1113]

@sorah Thanks to reply.

I believe this is sourced from https://github.com/interop-tokyo-shownet/ipaddr-ext and I noticed the difference in license.

Yes. this is sourced from ipaddr-ext gem, and it's a same author (me).
I guess to no problems merging it, because ipaddr-ext gem is licensed under the MIT license.

I'm also interested in upstreaming of other extensions in ipaddr-ext to ruby/ipaddr if you'd like…!

Thanks! I will try to create PR for other extensions of ipaddr-ext gem.