tailcfg: add Node.HasCap helpers

This makes a follow up change less noisy.

Updates #cleanup

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/ipnlocal/local.go

@@ -4094,8 +4094,8 @@ func (b *LocalBackend) setNetInfo(ni *tailcfg.NetInfo) {
 }
 
 func hasCapability(nm *netmap.NetworkMap, cap tailcfg.NodeCapability) bool {
-	if nm != nil && nm.SelfNode.Valid() {
-		return views.SliceContains(nm.SelfNode.Capabilities(), cap)
+	if nm != nil {
+		return nm.SelfNode.HasCap(cap)
 	}
 	return false
 }

ipn/ipnlocal/peerapi.go

@@ -1035,7 +1035,7 @@ func (h *peerAPIHandler) canPutFile() bool {
 // canDebug reports whether h can debug this node (goroutines, metrics,
 // magicsock internal state, etc).
 func (h *peerAPIHandler) canDebug() bool {
-	if !views.SliceContains(h.selfNode.Capabilities(), tailcfg.CapabilityDebug) {
+	if !h.selfNode.HasCap(tailcfg.CapabilityDebug) {
 		// This node does not expose debug info.
 		return false
 	}

ipn/ipnstate/ipnstate.go

@@ -291,6 +291,11 @@ type PeerStatus struct {
 	Location *tailcfg.Location `json:",omitempty"`
 }
 
+// HasCap reports whether ps has the given capability.
+func (ps *PeerStatus) HasCap(cap tailcfg.NodeCapability) bool {
+	return slices.Contains(ps.Capabilities, cap)
+}
+
 // StatusBuilder is a request to construct a Status. A new StatusBuilder is
 // passed to various subsystems which then call methods on it to populate state.
 // Call its Status method to return the final constructed Status.