tools: ynl: add uns-admin-perm to genetlink

tools: ynl: add uns-admin-perm to genetlink

GENL_UNS_ADMIN_PERM may be required by protocols using
the `genetlink` family, however, this flag is currently
only allowed in `genetlink-legacy`.

Add it to the list of possible values in genetlink.yaml too.

Cc: Simon Horman <horms@kernel.org>
Cc: Donald Hunter <donald.hunter@gmail.com>
Link: https://github.com/OpenVPN/ovpn-net-next/issues/33
Suggested-by: Ralf Lici <ralf@mandelbit.com>
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Link: https://patch.msgid.link/20260304141020.23270-1-antonio@openvpn.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>