mac80211_hwsim: make multi-channel ops const

Instead of building the multi-channel ops at runtime, declare
the common ops with a macro and build both that way, so that
the multi-channel ops can also be const.

As a side effect, due to the removed code, this decreases the
size of the module (while shifting data from .bss to .text
due to the newly added const).

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