types/netmap,wgengine/magicsock: propagate CapVer to magicsock.endpoint (#16244)

This enables us to mark nodes as relay capable or not. We don't actually
do that yet, as we haven't established a relay CapVer.

Updates tailscale/corp#27502

Signed-off-by: Jordan Whited <jordan@tailscale.com>

wgengine/magicsock/magicsock.go

@@ -2507,6 +2507,11 @@ func (c *Conn) SetProbeUDPLifetime(v bool) {
 	})
 }
 
+func capVerIsRelayCapable(version tailcfg.CapabilityVersion) bool {
+	// TODO(jwhited): implement once capVer is bumped
+	return false
+}
+
 // SetNetworkMap is called when the control client gets a new network
 // map from the control server. It must always be non-nil.
 //
@@ -3203,6 +3208,10 @@ func (c *Conn) UpdateNetmapDelta(muts []netmap.NodeMutation) (handled bool) {
 			ep.mu.Lock()
 			ep.setEndpointsLocked(views.SliceOf(m.Endpoints))
 			ep.mu.Unlock()
+		case netmap.NodeMutationCap:
+			ep.mu.Lock()
+			ep.relayCapable = capVerIsRelayCapable(m.Cap)
+			ep.mu.Unlock()
 		}
 	}
 	return true