netfilter: nf_tables: bogus EBUSY when deleting flowtable after flush

From: Laura Garcia Liebana <nevola@gmail.com>

commit 9b05b6e11d5e93a3a517cadc12b9836e0470c255 upstream.

The deletion of a flowtable after a flush in the same transaction
results in EBUSY. This patch adds an activation and deactivation of
flowtables in order to update the _use_ counter.

Signed-off-by: Laura Garcia Liebana <nevola@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>