logd: propagate ::log status

Add a return value for the ::log() methods, this allows
us to optimize the wakeup for the readers to only occur
when the log message is actually placed.

This is for a future where we may dedupe identical log
messages, filter out log messages, and certainly if we
filter the messages out with an internal logd check of
__android_log_is_loggable().

Change-Id: I763b2a7c29502ab7fa0a5d5022c7b60244fcfde4
diff --git a/logd/LogBuffer.h b/logd/LogBuffer.h
index a29e015..9ee243d 100644
--- a/logd/LogBuffer.h
+++ b/logd/LogBuffer.h
@@ -48,9 +48,9 @@
     LogBuffer(LastLogTimes *times);
     void init();
 
-    void log(log_id_t log_id, log_time realtime,
-             uid_t uid, pid_t pid, pid_t tid,
-             const char *msg, unsigned short len);
+    int log(log_id_t log_id, log_time realtime,
+            uid_t uid, pid_t pid, pid_t tid,
+            const char *msg, unsigned short len);
     uint64_t flushTo(SocketClient *writer, const uint64_t start,
                      bool privileged,
                      int (*filter)(const LogBufferElement *element, void *arg) = NULL,