json: deal appropriately with multidevice in chain

json: deal appropriately with multidevice in chain

Chain device support is broken in JSON: listing does not include devices
and parser only deals with one single device.

Use existing json_parse_flowtable_devs() function, rename it to
json_parse_devs() to parse the device array.

Use the dev_array that contains the device names (as string) for the
listing.

Update incorrect .json-nft files in tests/shell.

Fixes: 3fdc7541fba0 ("src: add multidevice support for netdev chain")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>