netfilter: nft_meta: fix typo "CONFIG_NET_CLS_ROUTE"

There are two checks for CONFIG_NET_CLS_ROUTE, but the corresponding
Kconfig symbol was dropped in v2.6.39. Since the code guards access to
dst_entry.tclassid it seems CONFIG_IP_ROUTE_CLASSID should be used
instead.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>