feature/taildrop: move rest of Taildrop out of LocalBackend

Updates #12614

Change-Id: If451dec1d796f6a4216fe485975c87f0c62a53e5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Co-authored-by: Nick Khyl <nickk@tailscale.com>

types/netmap/netmap.go

@@ -148,6 +148,14 @@ func (nm *NetworkMap) GetIPVIPServiceMap() IPServiceMappings {
 	return res
 }
 
+// SelfNodeOrZero returns the self node, or a zero value if nm is nil.
+func (nm *NetworkMap) SelfNodeOrZero() tailcfg.NodeView {
+	if nm == nil {
+		return tailcfg.NodeView{}
+	}
+	return nm.SelfNode
+}
+
 // AnyPeersAdvertiseRoutes reports whether any peer is advertising non-exit node routes.
 func (nm *NetworkMap) AnyPeersAdvertiseRoutes() bool {
 	for _, p := range nm.Peers {