support unusual IPv4 and IPv6 notations

[Abdull]

IPv4 and IPv6 addresses can be expressed in different notations. I noticed that ipcalc in version 0.51 does not support many of them.

Example addresses that fail with ipcalc 0.51 ("INVALID ADDRESS: ..."), but work with ping (from iputils 20210202 on Debian 11 bullseye 5.10.0-25-amd64):

127.1            # skipping zeros
0177.0x1    # using octal (0<number>) and hexadecimal (0x<number>)
127.999          # overflow into next octet
2130706433       # not using octet grouping

See:

• Fun with IP address parsing
  • Hacker News discussion: https://news.ycombinator.com/item?id=25545967
• Having fun with unusual IPv4 formats
• https://stackoverflow.com/questions/10133820/is-there-any-documentation-for-omitting-zeroes-in-dot-decimal-notation-of-ipv4-a
• https://superuser.com/questions/614001/why-can-i-ping-127-1