wifi: wext/libipw: move spy implementation to libipw
There's no driver left using this other than ipw2200,
so move the data bookkeeping and code into libipw.
Link: https://patch.msgid.link/20241007210254.037d864cda7d.Ib2197cb056ff05746d3521a5fba637062acb7314@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>