iwlwifi: mvm: check TLV flag before trying to use hotspot firmware commands

Older firmwares do not provide support for the HOT_SPOT_CMD command.
Check for the appropriate TLV flag that declares hotspot support in
the firmware to prevent a firmware assertion failure that can be
triggered from the userspace,

Cc: stable@vger.kernel.org [3.17+]
Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>