Disable sockaddr_nl on musl target

 See https://github.com/rust-lang-nursery/libc/pull/50 for details

libc-test/build.rs

@@ -108,7 +108,10 @@ fn main() {
         cfg.header("net/ethernet.h");
         cfg.header("malloc.h");
         cfg.header("sys/prctl.h");
-        cfg.header("linux/netlink.h");
+        /* linux kernel header */
+        if !musl {
+            cfg.header("linux/netlink.h");
+        }
     }
 
     if freebsd {
@@ -178,6 +181,13 @@ fn main() {
         }
     });
 
+    cfg.skip_struct(move |ty| {
+        match ty {
+            "sockaddr_nl" => musl,
+            _ => false
+        }
+    });
+
     cfg.skip_signededness(|c| {
         match c {
             "LARGE_INTEGER" |