net: ieee802154: Fix compilation error when CONFIG_IEEE802154_NL802154_EXPERIMENTAL is disabled

When CONFIG_IEEE802154_NL802154_EXPERIMENTAL is disabled,
NL802154_CMD_DEL_SEC_LEVEL is undefined and results in a compilation
error:
net/ieee802154/nl802154.c:2503:19: error: 'NL802154_CMD_DEL_SEC_LEVEL' undeclared here (not in a function); did you mean 'NL802154_CMD_SET_CCA_ED_LEVEL'?
 2503 |  .resv_start_op = NL802154_CMD_DEL_SEC_LEVEL + 1,
      |                   ^~~~~~~~~~~~~~~~~~~~~~~~~~
      |                   NL802154_CMD_SET_CCA_ED_LEVEL

Unhide the experimental commands, having them defined in an enum
makes no difference.

Fixes: 9c5d03d3 ("genetlink: start to validate reserved header bytes")
Signed-off-by: Gal Pressman <gal@nvidia.com>
Acked-by: Stefan Schmidt <stefan@datenfreihafen.org>
Tested-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Link: https://lore.kernel.org/r/20220902030620.2737091-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>