nl80211: fix non-split wiphy information

nl80211: fix non-split wiphy information

When dumping wiphy information, we try to split the data into
many submessages, but for old userspace we still support the
old mode where this doesn't happen.

However, in this case we were not resetting our state correctly
and dumping multiple messages for each wiphy, which would have
broken such older userspace.

This was broken pretty much immediately afterwards because it
only worked in the original commit where non-split dumps didn't
have any more data than split dumps...

Fixes: 2a4501502960 ("nl80211: re-add channel width and extended capa advertising")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20200928130717.3e6d9c6bada2.Ie0f151a8d0d00a8e1e18f6a8c9244dd02496af67@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>