wgengine/magicsock: rebind on EPIPE/ECONNRESET

Observed in the wild some macOS machines gain broken sockets coming out
of sleep (we observe "time jumped", followed by EPIPE on sendto). The
cause of this in the platform is unclear, but the fix is clear: always
rebind if the socket is broken. This can also be created artificially on
Linux via `ss -K`, and other conditions or software on a system could
also lead to the same outcomes.

Updates tailscale/corp#25648

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

wgengine/magicsock/magicsock_plan9.go

@@ -0,0 +1,12 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build plan9
+
+package magicsock
+
+// maybeRebindOnError performs a rebind and restun if the error is defined and
+// any conditionals are met.
+func (c *Conn) maybeRebindOnError(os string, err error) bool {
+	return false
+}