logd: replace internal CLOCK_MONOTONIC use with sequence numbers

- switch to simpler and faster internal sequence number, drops
  a syscall overhead on 32-bit platforms.
- add ability to break-out of flushTo loop with filter return -1
  allowing in reduction in reader overhead.

Change-Id: Ic5cb2b9afa4d9470153971fc9197b07279e2b79d
diff --git a/logd/FlushCommand.h b/logd/FlushCommand.h
index f34c06a..61c6858 100644
--- a/logd/FlushCommand.h
+++ b/logd/FlushCommand.h
@@ -31,7 +31,7 @@
     unsigned long mTail;
     unsigned int mLogMask;
     pid_t mPid;
-    log_time mStart;
+    uint64_t mStart;
 
 public:
     FlushCommand(LogReader &mReader,
@@ -39,7 +39,7 @@
                  unsigned long tail = -1,
                  unsigned int logMask = -1,
                  pid_t pid = 0,
-                 log_time start = LogTimeEntry::EPOCH);
+                 uint64_t start = 1);
     virtual void runSocketCommand(SocketClient *client);
 
     static bool hasReadLogs(SocketClient *client);