mac80211_hwsim: allow configurable cipher types

The mac80211_hwsim driver does not specify supported cipher types, which
in turn enables all ciphers to be supported in software. (see
net/mac80211/main.c:ieee80211_init_cipher_suites). Allowing ciphers
to be configurable is valuable for simulating older drivers that may
not support all ciphers.

This patch adds a new attribute:

 - HWSIM_ATTR_CIPHER_SUPPORT
	A u32 array/list of supported cipher types

This only allows enabling/disabling cipher types listed in the (new)
"hwsim_ciphers" array in mac80211_hwsim.c. Any unknown cipher type
will result in -EINVAL.

Signed-off-by: James Prestwood <james.prestwood@linux.intel.com>
[fix some indentation, change to hwsim_known_ciphers(),
 add error messages, validate length better]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>