Revert "ipn/ipnlocal: remove locks around sync.Cond.Broadcast call"

Reason for revert: Causes ipnlocal tests to deadlock intermittently.

This reverts commit 1b15349e01.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

ipn/ipnlocal/local.go

@@ -601,12 +601,18 @@ func (b *LocalBackend) findExitNodeIDLocked(nm *netmap.NetworkMap) (prefsChanged
 func (b *LocalBackend) setWgengineStatus(s *wgengine.Status, err error) {
 	if err != nil {
 		b.logf("wgengine status error: %v", err)
+
+		b.statusLock.Lock()
 		b.statusChanged.Broadcast()
+		b.statusLock.Unlock()
 		return
 	}
 	if s == nil {
 		b.logf("[unexpected] non-error wgengine update with status=nil: %v", s)
+
+		b.statusLock.Lock()
 		b.statusChanged.Broadcast()
+		b.statusLock.Unlock()
 		return
 	}
 
@@ -626,7 +632,11 @@ func (b *LocalBackend) setWgengineStatus(s *wgengine.Status, err error) {
 		}
 		b.stateMachine()
 	}
+
+	b.statusLock.Lock()
 	b.statusChanged.Broadcast()
+	b.statusLock.Unlock()
+
 	b.send(ipn.Notify{Engine: &es})
 }