docs: net: 80211: reduce docs build time

the files under /80211 calls kernel-doc script 207 times, one for each
single function and doc chapter. Due to that, it takes a lot of time
handling it:

	$ touch Documentation/driver-api/80211/*rst && time make SPHINXDIRS=driver-api/80211 htmldocs
...
	real	0m22,928s
	user	0m21,644s
	sys	0m1,334s

Reduce the build time by doing only one kernel-doc call
per functions that belong to the same group. With that, there's now
50 calls to kernel-doc, which makes the build time for those docs
62% faster:

	$ touch Documentation/driver-api/80211/*rst && time make SPHINXDIRS=driver-api/80211 htmldocs
...
	real	0m8,666s
	user	0m8,084s
	sys	0m0,642s

As a side effect, it should now be easier to add newer
functions, as there's no need to repeat the kernel-doc
pattern.

Measurements made on a NUC8i7HNK machine with lots of ram
and a fast SSD disk with Sphinx 3.2.1.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/f0085721d85ebc3a77164b457ed948eee48b55df.1601890703.git.mchehab+huawei@kernel.org


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