all: use iterators in more places instead of Range funcs

And misc cleanup along the way.

Updates #12912

Change-Id: I0cab148b49efc668c6f5cdf09c740b84a713e388
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

types/netmap/netmap.go

@@ -197,21 +197,11 @@ func (nm *NetworkMap) DomainName() string {
 	return nm.Domain
 }
 
-// SelfCapabilities returns SelfNode.Capabilities if nm and nm.SelfNode are
-// non-nil. This is a method so we can use it in envknob/logknob without a
-// circular dependency.
-func (nm *NetworkMap) SelfCapabilities() views.Slice[tailcfg.NodeCapability] {
-	var zero views.Slice[tailcfg.NodeCapability]
-	if nm == nil || !nm.SelfNode.Valid() {
-		return zero
-	}
-	out := nm.SelfNode.Capabilities().AsSlice()
-	nm.SelfNode.CapMap().Range(func(k tailcfg.NodeCapability, _ views.Slice[tailcfg.RawMessage]) (cont bool) {
-		out = append(out, k)
-		return true
-	})
-
-	return views.SliceOf(out)
+// HasSelfCapability reports whether nm.SelfNode contains capability c.
+//
+// It exists to satisify an unused (as of 2025-01-04) interface in the logknob package.
+func (nm *NetworkMap) HasSelfCapability(c tailcfg.NodeCapability) bool {
+	return nm.AllCaps.Contains(c)
 }
 
 func (nm *NetworkMap) String() string {