std::net: fix Ipv4Addr::is_global()

As per @therealbstern's comment[0]:

The implementation of Ipv4::is_global is not complete, according to the
IANA IPv4 Special-Purpose Address Registry.

        - It compares the address to 0.0.0.0, but anything in 0.0.0.0/8
          should not be considered global.
                - 0/8 is not global and is currently forbidden because
                  some systems used to treat it as the local network.
                - The implementation of Ipv4::is_unspecified is correct.
                  0.0.0.0 is the unspecified address.
        - It does not examine 100.64.0.0/10, which is "Shared Address
          Space" and not global.
        - Ditto 192.0.0.0/24 (IETF Protocol Assignments), except for
          192.0.0.9/32 and 192.0.0.10/32, which are carved out as
          globally reachable.
        - 198.18.0.0/15 is for "Benchmarking" and should not be globally
          reachable.
        - 240.0.0.0/4 is reserved and not currently reachable

0 files changed, 0 insertions, 0 deletions