lib/channel_helper: Lwt_unix requires bytes
lib/channel_helper: Lwt_unix requires bytes

I was surprised that the compiler did not complain (safe-string was on)

Signed-off-by: Marcello Seri <34fd14c67154e888f6587d5c0e7eadd13aaf7ca7@citrix.com>

xapi-project/message-switch,xapi-project/message-switch,xapi-project/message-switch