HS 2.0: Allow configuration of operator icons

HS 2.0: Allow configuration of operator icons

This extends hostapd Hotspot 2.0 implementation to allow operator icons
to be made available. The existing hs20_icon parameter is used to define
the icons and the new operator_icon parameter (zero or more entries) is
used to specify which of the available icons are operator icons. The
operator icons are advertised in the Operator Icon Metadata ANQP-element
while the icon data can be fetched using the same mechanism (icon
request/binary file) that was added for the OSU Providers icons.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>