Remove the meaningless on Linux if_dl.h header.

This was misleading 'configure' into thinking we actually support AF_LINK,
but we're Linux, so we don't, and we never implemented the functions we
declared here either.

Reported to AOSP by Jun-ya Kato.

Change-Id: I111f9887f3812469b411b9cf5124d9dd624f19f7
diff --git a/libc/netbsd/net/getnameinfo.c b/libc/netbsd/net/getnameinfo.c
index 8a1e95e..d8ac037 100644
--- a/libc/netbsd/net/getnameinfo.c
+++ b/libc/netbsd/net/getnameinfo.c
@@ -53,7 +53,9 @@
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <net/if.h>
+#if defined(ANDROID_CHANGES) && defined(AF_LINK)
 #include <net/if_dl.h>
+#endif
 #include <net/if_ieee1394.h>
 #include <net/if_types.h>
 #include <netinet/in.h>
@@ -104,8 +106,10 @@
 static int ip6_sa2str __P((const struct sockaddr_in6 *, char *, size_t,
 				 int));
 #endif
+#if defined(ANDROID_CHANGES) && defined(AF_LINK)
 static int getnameinfo_link __P((const struct sockaddr *, socklen_t, char *,
     socklen_t, char *, socklen_t, int));
+#endif
 static int hexname __P((const u_int8_t *, size_t, char *, socklen_t));
 
 // This should be synchronized to ResponseCode.h
@@ -123,7 +127,7 @@
 	case AF_INET6:
 		return getnameinfo_inet(sa, salen, host, hostlen,
 		    serv, servlen, flags);
-#if 0
+#if defined(ANDROID_CHANGES) && defined(AF_LINK)
 	case AF_LINK:
 		return getnameinfo_link(sa, salen, host, hostlen,
 		    serv, servlen, flags);
@@ -408,7 +412,7 @@
 #endif
 
 		if (hp) {
-#if 0
+#if defined(ANDROID_CHANGES) && defined(AF_LINK)
 			/*
 			 * commented out, since "for local host" is not
 			 * implemented here - see RFC2553 p30
@@ -546,6 +550,7 @@
 #endif /* INET6 */
 
 
+#if defined(ANDROID_CHANGES) && defined(AF_LINK)
 /*
  * getnameinfo_link():
  * Format a link-layer address into a printable format, paying attention to
@@ -623,6 +628,7 @@
 		    (size_t)sdl->sdl_alen, host, hostlen);
 	}
 }
+#endif
 
 static int
 hexname(cp, len, host, hostlen)