Stop using the __ANDROID_API_x__ constants.

Historically we've made a few mistakes where they haven't matched the
right number. And most non-Googlers are much more familiar with the
numbers, so it seems to make sense to rely more on them. Especially in
header files, which we actually expect real people to have to read from
time to time.

Test: treehugger
Change-Id: I0d4a97454ee108de1d32f21df285315c5488d886
diff --git a/libc/include/netinet/in.h b/libc/include/netinet/in.h
index 1c9961c..7f00a7a 100644
--- a/libc/include/netinet/in.h
+++ b/libc/include/netinet/in.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _NETINET_IN_H_
-#define _NETINET_IN_H_
+#pragma once
 
 #include <endian.h>
 #include <netinet/in6.h>
@@ -46,14 +45,12 @@
 
 int bindresvport(int __fd, struct sockaddr_in* __sin);
 
-#if __ANDROID_API__ >= __ANDROID_API_N__
+#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__ >= __ANDROID_API_N__ */
+#endif
 
 __END_DECLS
-
-#endif