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.x86.map b/libc/libc.x86.map
index bcabf71..6e32978 100644
--- a/libc/libc.x86.map
+++ b/libc/libc.x86.map
@@ -233,10 +233,6 @@
     alarm;
     alphasort;
     alphasort64;
-    android_getaddrinfofornet;
-    android_getaddrinfofornetcontext;
-    android_gethostbyaddrfornet;
-    android_gethostbynamefornet;
     android_set_abort_message;
     arc4random;
     arc4random_buf;
@@ -1276,6 +1272,10 @@
     __umoddi3; # x86 mips
     __wait4; # arm x86 mips nobrillo
     _fwalk; # arm x86 mips
+    android_getaddrinfofornet;
+    android_getaddrinfofornetcontext;
+    android_gethostbyaddrfornet;
+    android_gethostbynamefornet;
     arc4random_addrandom; # arm x86 mips nobrillo
     arc4random_stir; # arm x86 mips nobrillo
     bcopy; # arm x86 mips nobrillo