onewire_parser: Keep server handle open at all time

onewire_parser: Keep server handle open at all time

On libowfs 2.7 there appear to be a problem when releasing the client
resources. At least sockets are left open every now and then. There is
no such problem with 3.1 version.

To resolve the issue with older client library, keep the serve handle
open at all time. Release it only when there is a change with the
server address, which normally does not happen ever.

Signed-off-by: Timo Kokkonen <timo.t.kokkonen@iki.fi>