Migrate net.tcp.default_init_rwnd to net.tcp_def_init_rwnd

Currently, tcp receive window size is read from
net.tcp.default_init_rwnd then set to net.tcp_def_init_rwnd. It
should not use seperate property to read/write the value, it only
needs one of property basically. So migrate
net.tcp.default_init_rwnd to net.tcp_def_init_rwnd which has
formal API.

Bug: 182538166
Test: Manually check that net.tcp_def_init_rwnd has default
      value and proc/sys/net/ipv4/tcp_default_inti_rwnd node
      is created with same value.
Change-Id: I6748485f99198b1200c67d6595b659aac7d7e1e0
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 58e161d..11b3da7 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -1074,7 +1074,7 @@
     chown root radio /proc/cmdline
 
     # Define default initial receive window size in segments.
-    setprop net.tcp.default_init_rwnd 60
+    setprop net.tcp_def_init_rwnd 60
 
     # Start standard binderized HAL daemons
     class_start hal