set /proc/sys/net/unix/max_dgram_qlen to large value

- init: set /proc/sys/net/unix/max_dgram_qlen to 300
- libsysutils: Add listen backlog argument to startListener
- logd: set listen backlog to 300

Change-Id: Id6d37d6c937ba2d221e76258d89c9516619caeec
diff --git a/logd/main.cpp b/logd/main.cpp
index 1891206..6216b95 100644
--- a/logd/main.cpp
+++ b/logd/main.cpp
@@ -105,7 +105,8 @@
     // and LogReader is notified to send updates to connected clients.
 
     LogListener *swl = new LogListener(logBuf, reader);
-    if (swl->startListener()) {
+    // Backlog and /proc/sys/net/unix/max_dgram_qlen set to large value
+    if (swl->startListener(300)) {
         exit(1);
     }