netfilter: nf_tables: disallow NFT_SET_ELEM_CATCHALL and NFT_SET_ELEM_INTERVAL_END

These flags are mutually exclusive, report EINVAL in this case.

Fixes: aaa31047 ("netfilter: nftables: add catch-all set element support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>