If the context given to DialContext has a shorter lifetime than the OS
TCP SYN timeout, and TCP SYNs are dropped from the path to the remote,
DialContext would never fall back to try IPv6 after IPv4.
Instead, use the normal happy eyeballs race if there is more than one
address. This does remove the implicit prioritization of IPv4 over IPv6
in cases where there is only a single IPv4 remote address.
Updates #13346
Signed-off-by: Claus Lensbøl <claus@tailscale.com>
ee0a03b140