Revert "all: keep UserProfiles a slice instead of a map for longer"

This reverts commit e5894aba42.

Breaks macOS/iOS build. Reverting per chat with Josh; he'll fix later today.

ipn/ipnstate/ipnstate.go

@@ -112,7 +112,7 @@ func (sb *StatusBuilder) SetSelfStatus(ss *PeerStatus) {
 }
 
 // AddUser adds a user profile to the status.
-func (sb *StatusBuilder) AddUser(up tailcfg.UserProfile) {
+func (sb *StatusBuilder) AddUser(id tailcfg.UserID, up tailcfg.UserProfile) {
 	sb.mu.Lock()
 	defer sb.mu.Unlock()
 	if sb.locked {
@@ -124,7 +124,7 @@ func (sb *StatusBuilder) AddUser(up tailcfg.UserProfile) {
 		sb.st.User = make(map[tailcfg.UserID]tailcfg.UserProfile)
 	}
 
-	sb.st.User[up.ID] = up
+	sb.st.User[id] = up
 }
 
 // AddIP adds a Tailscale IP address to the status.

ipn/local.go

@@ -163,8 +163,8 @@ func (b *LocalBackend) UpdateStatus(sb *ipnstate.StatusBuilder) {
 	// TODO: hostinfo, and its networkinfo
 	// TODO: EngineStatus copy (and deprecate it?)
 	if b.netMap != nil {
-		for _, up := range b.netMap.UserProfiles {
-			sb.AddUser(up)
+		for id, up := range b.netMap.UserProfiles {
+			sb.AddUser(id, up)
 		}
 		for _, p := range b.netMap.Peers {
 			var lastSeen time.Time