netfilter: nf_tables: fix bogus warning in nft_data_uninit()

The values 0x00000000-0xfffffeff are reserved for userspace datatype. When,
deleting set elements with maps, a bogus warning is triggered.

WARNING: CPU: 0 PID: 11133 at net/netfilter/nf_tables_api.c:4481 nft_data_uninit+0x35/0x40 [nf_tables]()

This fixes the check accordingly to enum definition in
include/linux/netfilter/nf_tables.h

Fixes: https://bugzilla.netfilter.org/show_bug.cgi?id=1013
Signed-off-by: Mirek Kratochvil <exa.exa@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>