sysx/xattr: fix getxattrAll
sysx/xattr: fix getxattrAll

The current implementation is suboptimal for two reasons:

 * the initial buffer size of 5 bytes makes no sense
   (my guess someone forgot to change it back to a sane
   value after the retry logic testing);

 * it never gets the real buffer size, resulting in extra
   iterations (5 -> 10 -> 20 -> ...).

This commit
 * sets the initial size to 128;
 * uses the logic to get the real size in case we get ERANGE

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

stevvooe/continuity,containerd/continuity,stevvooe/continuity