Change lmkd defaults for statsd events

LMK events are an important platform memory monitoring signal. Enable
them by default.
Changes:
- Compile lmkd with statsd by default
- Signal lmkd by default

Test: build, statsd cts
Bug: 177985094
Change-Id: I070660767db6e3bc8926ff82b64b99c7ee9a0108

Android.bp

@@ -1,13 +1,8 @@
 cc_defaults {
     name: "stats_defaults",
-
-    product_variables: {
-        use_lmkd_stats_log: {
-            cflags: [
-                "-DLMKD_LOG_STATS"
-            ],
-        },
-    },
+    cflags: [
+        "-DLMKD_LOG_STATS"
+    ],
 }
 
 cc_binary {

statslog.cpp

@@ -34,7 +34,7 @@
 #define STRINGIFY(x) STRINGIFY_INTERNAL(x)
 #define STRINGIFY_INTERNAL(x) #x
 
-static bool enable_stats_log = property_get_bool("ro.lmk.log_stats", false);
+static bool enable_stats_log = property_get_bool("ro.lmk.log_stats", true);
 
 struct proc {
     int pid;