adding if_nameindex/if_freenameindex support for Android.

[ref](https://android.googlesource.com/platform/bionic/+/master/libc/include/net/if.h#52)

close rust-langGH-4246

(backport <rust-lang#4247>)
(cherry picked from commit 32821d4)

Author: devnexen

libc-test/build.rs

@@ -1906,6 +1906,8 @@ fn test_android(target: &str) {
 
             // FIXME(android): "'__uint128' undeclared" in C
             "__uint128" => true,
+            // Added in API level 24
+            "if_nameindex" => true,
 
             _ => false,
         }
@@ -2152,6 +2154,9 @@ fn test_android(target: &str) {
             | "ispunct" | "isspace" | "isupper" | "isxdigit" | "isblank" | "tolower"
             | "toupper" => true,
 
+            // Added in API level 24
+            "if_nameindex" | "if_freenameindex" => true,
+
             _ => false,
         }
     });

libc-test/semver/android.txt

@@ -3382,7 +3382,9 @@ group
 hostent
 id_t
 idtype_t
+if_freenameindex
 if_indextoname
+if_nameindex
 if_nametoindex
 ifaddrs
 ifconf

src/unix/linux_like/android/mod.rs

@@ -517,6 +517,11 @@ s! {
         pub ifr6_prefixlen: u32,
         pub ifr6_ifindex: c_int,
     }
+
+    pub struct if_nameindex {
+        pub if_index: c_uint,
+        pub if_name: *mut c_char,
+    }
 }
 
 s_no_extra_traits! {
@@ -4136,6 +4141,9 @@ extern "C" {
         newpath: *const c_char,
         flags: c_uint,
     ) -> c_int;
+
+    pub fn if_nameindex() -> *mut if_nameindex;
+    pub fn if_freenameindex(ptr: *mut if_nameindex);
 }
 
 cfg_if! {