wgengine/magicsock: fix rebind debouncing (#17282)

On platforms that are causing EPIPE at a high frequency this is
resulting in non-working connections, for example when Apple decides to
forcefully close UDP sockets due to an unsoliced packet rejection in the
firewall.

Too frequent rebinds cause a failure to solicit the endpoints triggering
the rebinds, that would normally happen via CallMeMaybe.

Updates #14551
Updates tailscale/corp#25648

Signed-off-by: James Tucker <james@tailscale.com>

wgengine/magicsock/magicsock.go

@@ -1563,6 +1563,7 @@ func (c *Conn) maybeRebindOnError(err error) {
 
 	if c.lastErrRebind.Load().Before(time.Now().Add(-5 * time.Second)) {
 		c.logf("magicsock: performing rebind due to %q", reason)
+		c.lastErrRebind.Store(time.Now())
 		c.Rebind()
 		go c.ReSTUN(reason)
 	} else {