src: queue: consolidate queue statement syntax

src: queue: consolidate queue statement syntax

Print queue statement using the 'queue ... to' syntax to consolidate the
syntax around Florian's proposal introduced in 6cf0f2c17bfb ("src:
queue: allow use of arbitrary queue expressions").

Retain backward compatibility, 'queue num' syntax is still allowed.

Update and add new tests.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>