nl80211: increase wiphy dump size dynamically

nl80211: increase wiphy dump size dynamically

Given a device with many channels capabilities the wiphy
information can still overflow even though its size in
3.9 was reduced to 3.8 levels. For new userspace and
kernel 3.10 we're going to implement a new "split dump"
protocol that can use multiple messages per wiphy.

For now though, add a workaround to be able to send more
information to userspace. Since generic netlink doesn't
have a way to set the minimum dump size globally, and we
wouldn't really want to set it globally anyway, increase
the size only when needed, as described in the comments.
As userspace might not be prepared for large buffers, we
can only use 4k.

Also increase the size for the get_wiphy command.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>