all: add (*testing.B).ReportAllocs() to every benchmark

This ensures that we can properly track and catch allocation
slippages that could otherwise have been missed.

Fixes #2748

net/tsaddr/tsaddr_test.go

@@ -75,6 +75,7 @@ func TestNewContainsIPFunc(t *testing.T) {
 var sinkIP netaddr.IP
 
 func BenchmarkTailscaleServiceAddr(b *testing.B) {
+	b.ReportAllocs()
 	for i := 0; i < b.N; i++ {
 		sinkIP = TailscaleServiceIP()
 	}