Add ip_mreqn on Android

This was added to Android's libc (bionic) in 2013. See
https://cs.android.com/android/_/android/platform/bionic/+/655a7c081f83b8351ed5f11a6c6accd9458293a8.

Author: tamird

libc-test/semver/android.txt

@@ -2844,6 +2844,7 @@ intptr_t
 ioctl
 iovec
 ip_mreq
+ip_mreqn
 ip_mreq_source
 ipv6_mreq
 isalnum

src/unix/linux_like/android/mod.rs

@@ -73,6 +73,12 @@ s! {
         pub cmsg_type: ::c_int,
     }
 
+    pub struct ip_mreqn {
+        pub imr_multiaddr: ::in_addr,
+        pub imr_address: ::in_addr,
+        pub imr_ifindex: ::c_int,
+    }
+
     pub struct termios {
         pub c_iflag: ::tcflag_t,
         pub c_oflag: ::tcflag_t,