To support IPv6, Git provided fall back functions for Windows versions that
did not support IPv6. However, as Git dropped support for Windows XP and
prior, those functions are not needed anymore.
Removed those fallbacks by reverting commit[1] and using the functions
directly (without 'ipv6_' prefix).
[1] fe3b2b7b82.
Signed-off-by: tanushree27 <tanushreetumane@gmail.com>