Move android_ network functions to LIBC_PRIVATE

Make following functions platform-private:
 android_getaddrinfofornet
 android_getaddrinfofornetcontext
 android_gethostbyaddrfornet
 android_gethostbynamefornet

Bug: http://b/26794226
Change-Id: I0855b0b82721e4d24e918508931b4d5587fcae7d
diff --git a/libc/libc.arm.brillo.map b/libc/libc.arm.brillo.map
index 95f7cba..7677980 100644
--- a/libc/libc.arm.brillo.map
+++ b/libc/libc.arm.brillo.map
@@ -234,10 +234,6 @@
     alarm;
     alphasort;
     alphasort64;
-    android_getaddrinfofornet;
-    android_getaddrinfofornetcontext;
-    android_gethostbyaddrfornet;
-    android_gethostbynamefornet;
     android_set_abort_message;
     arc4random;
     arc4random_buf;
@@ -1421,6 +1417,10 @@
     _Unwind_VRS_Get; # arm
     _Unwind_VRS_Pop; # arm
     _Unwind_VRS_Set; # arm
+    android_getaddrinfofornet;
+    android_getaddrinfofornetcontext;
+    android_gethostbyaddrfornet;
+    android_gethostbynamefornet;
     atexit; # arm
     free_malloc_leak_info;
     get_malloc_leak_info;