AIX doesn't set OptionLength for boolean options

https://rubyci.org/logs/rubyci.s3.amazonaws.com/aix71_ppc/ruby-trunk/log/20180904T103302Z.fail.html.gz
https://www.ibm.com/support/knowledgecenter/ja/ssw_aix_72/com.ibm.aix.commtrf2/getsockopt.htm

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64636 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/socket/basicsocket.c

@@ -314,6 +314,18 @@ bsock_getsockopt(VALUE sock, VALUE lev, VALUE optname)
     level = rsock_level_arg(family, lev);
     option = rsock_optname_arg(family, level, optname);
     len = 256;
+#ifdef Qnil
+    switch (option) {
+      case SO_DEBUG:
+      case SO_REUSEADDR:
+      case SO_KEEPALIVE:
+      case SO_DONTROUTE:
+      case SO_BROADCAST:
+      case SO_OOBINLINE:
+        /* AIX doesn' set len for boolean options */
+        len = sizeof(int);
+    }
+#endif
     buf = ALLOCA_N(char,len);
 
     rb_io_check_closed(fptr);