chardev: add nodelay option

chardev: add nodelay option

The "delay" option was introduced as a way to enable Nagle's algorithm
with ",nodelay".  Since the short form for boolean options has now been
deprecated, introduce a more properly named "nodelay" option.  The "delay"
option remains as an undocumented option.

"delay" and "nodelay" are mutually exclusive.  Because the check is
done at consumption time, the code also rejects them if one of the
two is specified via -set.

Based-on: <20210226080526.651705-1-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>