iterate over hw-indexed hashtable, too
mac802154: allow only one WPAN to be up at any given time

All 802.15.4 PHY devices with drivers in tree can support only one WPAN
at any given time, yet the stack allows arbitrarily many WPAN devices to
be created and up at the same time. This cannot work with what the
hardware provides, and in the current implementation, provides an easy
DoS vector to any process on the system that may call socket() and
sendmsg().

Thus, allow only one WPAN per PHY to be up at once, just like mac80211
does for managed devices.

Signed-off-by: Phoebe Buckheister <phoebe.buckheister@itwm.fraunhofer.de>
mac802154: make csma/cca parameters per-wpan

Commit $me (...) erroneously added CSMA and CCA parameters for 8021.5.4
devices as PHY parameters, while they are actually MAC parameters and
can differ for any two WPAN instances. Since it is now sensible to have
multiple WPAN devices with differing CSMA/CCA parameters, make these
parameters MAC parameters instead.

Signed-off-by: Phoebe Buckheister <phoebe.buckheister@itwm.fraunhofer.de>
require only device address on remove