nl80211: Add support to set AP settings flags with single attribute

nl80211: Add support to set AP settings flags with single attribute

In previous method each AP settings flag is represented by a top-level
flag attribute and conversion to enum cfg80211_ap_settings_flags had to
be done before sending them to driver. This commit is to make it easier
to define new AP settings flags and sending them to driver.

This commit also deprecate sending of
%NL80211_ATTR_EXTERNAL_AUTH_SUPPORT in %NL80211_CMD_START_AP. But to
maintain backwards compatibility checks for
%NL80211_ATTR_EXTERNAL_AUTH_SUPPORT in %NL80211_CMD_START_AP when
%NL80211_ATTR_AP_SETTINGS_FLAGS not present in %NL80211_CMD_START_AP.

Signed-off-by: Veerendranath Jakkam <vjakkam@codeaurora.org>
Link: https://lore.kernel.org/r/1637911519-21306-1-git-send-email-vjakkam@codeaurora.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>