linux-user: fix mq_getsetattr implementation

mq_getsetattr implementation does not set errno correctly in case of
error. Also in the presence of both 2nd and 3rd arguments it calls both
mq_getattr and mq_setattr, whereas only the latter call would suffice.

Don't call mq_getattr in the presence of the 2nd argument. Don't copy
output back to user in case of error. Use get_errno to set errno value.

This fixes test rt/tst-mqueue2 from the glibc testsuite.

Cc: Lionel Landwerlin <lionel.landwerlin@openwide.fr>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Riku Voipio <riku.voipio@iki.fi>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>

linux-user/syscall.c

@@ -12092,15 +12092,16 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
         {
             struct mq_attr posix_mq_attr_in, posix_mq_attr_out;
             ret = 0;
-            if (arg3 != 0) {
-                ret = mq_getattr(arg1, &posix_mq_attr_out);
-                copy_to_user_mq_attr(arg3, &posix_mq_attr_out);
-            }
             if (arg2 != 0) {
                 copy_from_user_mq_attr(&posix_mq_attr_in, arg2);
-                ret |= mq_setattr(arg1, &posix_mq_attr_in, &posix_mq_attr_out);
+                ret = get_errno(mq_setattr(arg1, &posix_mq_attr_in,
+                                           &posix_mq_attr_out));
+            } else if (arg3 != 0) {
+                ret = get_errno(mq_getattr(arg1, &posix_mq_attr_out));
+            }
+            if (ret == 0 && arg3 != 0) {
+                copy_to_user_mq_attr(arg3, &posix_mq_attr_out);
             }
-
         }
         break;
 #endif