Provide static inlines for in6addr things.

mdnsresponder needs these and is built against a very old API level
since it is used in gmscore. The legacy NDK headers defined these
inline.

Test: make checkbuild
Bug: http://b/30465923
Change-Id: I92cd0116b3bde47e748ba648eaba94a7a3e3523e
diff --git a/libc/include/netinet/in.h b/libc/include/netinet/in.h
index 00b5cf9..3574976 100644
--- a/libc/include/netinet/in.h
+++ b/libc/include/netinet/in.h
@@ -47,8 +47,13 @@
 
 int bindresvport(int, struct sockaddr_in*);
 
+#if __ANDROID_API__ >= 24
 extern const struct in6_addr in6addr_any __INTRODUCED_IN(24);
 extern const struct in6_addr in6addr_loopback __INTRODUCED_IN(24);
+#else
+static const struct in6_addr in6addr_any = IN6ADDR_ANY_INIT;
+static const struct in6_addr in6addr_loopback = IN6ADDR_LOOPBACK_INIT;
+#endif /* __ANDROID_API__ >= 24 */
 
 __END_DECLS