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.map.txt b/libc/libc.map.txt
index 928f10d..35136fa 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -238,10 +238,6 @@
     alarm;
     alphasort;
     alphasort64;
-    android_getaddrinfofornet;
-    android_getaddrinfofornetcontext;
-    android_gethostbyaddrfornet;
-    android_gethostbynamefornet;
     android_set_abort_message;
     arc4random;
     arc4random_buf;
@@ -1461,6 +1457,10 @@
     _Unwind_VRS_Get; # arm
     _Unwind_VRS_Pop; # arm
     _Unwind_VRS_Set; # arm
+    android_getaddrinfofornet;
+    android_getaddrinfofornetcontext;
+    android_gethostbyaddrfornet;
+    android_gethostbynamefornet;
     arc4random_addrandom; # arm x86 mips nobrillo
     arc4random_stir; # arm x86 mips nobrillo
     atexit; # arm