netfilter: nf_tables: validate family when identifying table via handle

Validate table family when looking up for it via NFTA_TABLE_HANDLE.

Fixes: 3ecbfd65

 ("netfilter: nf_tables: allocate handle and delete objects via handle")
Reported-by: Xingyuan Mo <hdthky0@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>