netfilter: nft_compat: use-after-free when deleting targets

Fetch pointer to module before target object is released.

Fixes: 29e38801 ("netfilter: nf_tables: fix use-after-free when deleting compat expressions")
Fixes: 0ca743a5 ("netfilter: nf_tables: add compatibility layer for x_tables")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>