If we have a message without payload, we call full_read() with
len set to 0, which causes it to return -ECONNRESET. Catch this
case and explicitly return 0 for it so we can actually use the
zero-size config-changed message.
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NRichard Weinberger <richard@nod.at>