Solicited multicast-address creation bugfix

[NikitaKovaljov]

Fixes #16614

• This change is fixing solicited-multicast address creation, by finding leading zeros in last 16 bits of link-local address and removing them.

• This change is also follows with fully rewritten function to easier logic for understanding.

Reference to issue

• Fixes Improper solicited-multicast address generation in ipv6.rb  #16614

Verification

• copy ipv6_soll_mcast_addr6 function and make changes according to code down below and save it as ruby file:

def ipv6_soll_mcast_addr6(addr)
    h = addr.split(':')[-2, 2]
    m = []  
    x = h[0]
    x[0..1] = 'ff'
    m << x
    x = h[1]
    x.sub!(/^0*/, "")
    m << x
    puts 'ff02::1:' + m.join(':')
end

ipv6_soll_mcast_addr6("fe80::200:00ff:fe00:0002")

• run ruby file

ruby file_name.rb

• output

ff02::1:ff00:2

[gwillcox-r7]

Code seems to work and looks correct. Those wishing to understand it more are encouraged to look at https://www.networkcomputing.com/networking/understanding-ipv6-what-solicited-node-multicast which mentions http://datatracker.ietf.org/doc/rfc4291/ section 2.7.1 as stating that the range of a solicited node multicast is from FF02:0:0:0:0:1:FF00:0000 to FF02:0:0:0:0:1:FFFF:FFFF, and if we consider that we can omit the :0: parts to shorten the length of the address that we write, the code makes sense.

Will get this landed now.

[gwillcox-r7]

Release Notes

A bug has been fixed in the IPv6 library when creating solicited-multicast addresses by finding leading zeros in last 16 bits of link-local address and removing them.