LibC: Add INET_ADDRSTRLEN define

Author: https://github.com/rburchell
Commit: https://github.com/SerenityOS/serenity/commit/cf41b0ef175
Pull-request: https://github.com/SerenityOS/serenity/pull/45
Reviewed-by: https://github.com/awesomekling

LibC/arpa/inet.h

@@ -5,6 +5,8 @@
 
 __BEGIN_DECLS
 
+#define INET_ADDRSTRLEN 16
+
 const char* inet_ntop(int af, const void* src, char* dst, socklen_t);
 int inet_pton(int af, const char* src, void* dst);