wgengine/{magicsock,userspace,router}: move portupdates to the eventbus (#17423)

Also pull out interface method only needed in Linux.

Instead of having userspace do the call into the router, just let the
router pick up the change itself.

Updates #15160

Signed-off-by: Claus Lensbøl <claus@tailscale.com>

wgengine/router/callback.go

@@ -56,13 +56,6 @@ func (r *CallbackRouter) Set(rcfg *Config) error {
 	return r.SetBoth(r.rcfg, r.dcfg)
 }
 
-// UpdateMagicsockPort implements the Router interface. This implementation
-// does nothing and returns nil because this router does not currently need
-// to know what the magicsock UDP port is.
-func (r *CallbackRouter) UpdateMagicsockPort(_ uint16, _ string) error {
-	return nil
-}
-
 // SetDNS implements dns.OSConfigurator.
 func (r *CallbackRouter) SetDNS(dcfg dns.OSConfig) error {
 	r.mu.Lock()