wgengine/magicsock: add address selection for wireguard only endpoints (#7979)

This change introduces address selection for wireguard only endpoints.
If a endpoint has not been used before, an address is randomly selected
to be used based on information we know about, such as if they are able
to use IPv4 or IPv6. When an address is initially selected, we also
initiate a new ICMP ping to the endpoints addresses to determine which
endpoint offers the best latency. This information is then used to
update which endpoint we should be using based on the best possible
route. If the latency is the same for a IPv4 and an IPv6 address, IPv6
will be used.

Updates #7826

Signed-off-by: Charlotte Brandhorst-Satzkorn <charlotte@tailscale.com>

cmd/tailscaled/depaware.txt

@@ -245,7 +245,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
      💣 tailscale.com/net/netstat                                    from tailscale.com/ipn/ipnauth+
         tailscale.com/net/netutil                                    from tailscale.com/ipn/ipnlocal+
         tailscale.com/net/packet                                     from tailscale.com/net/tstun+
-        tailscale.com/net/ping                                       from tailscale.com/net/netcheck
+        tailscale.com/net/ping                                       from tailscale.com/net/netcheck+
         tailscale.com/net/portmapper                                 from tailscale.com/net/netcheck+
         tailscale.com/net/proxymux                                   from tailscale.com/cmd/tailscaled
         tailscale.com/net/routetable                                 from tailscale.com/doctor/routetable