Add nftables.Modifier, to hold a queue of commands that can be applied
using Modifier.Apply. No updates are made to the underlying Table
until Apply is called, errors in the queue if commands are deferred
until Apply.
This has the advantages that:
- less error handling is needed in code that generates update commands
- it's transactional, without needing explicit transactions
Minor disadvantages are that it's slightly more difficult to debug updates,
as it's no longer possible to step through the call making an update to
the Table manipulation in a debugger - and errors in the command, and
errors like trying to update a nonexistent chain/set/vmap, deleting an
object that doesn't exist or creating a duplicate are not reported
until the updates are applied (but, the file/line where the rule was
added is reported).
Signed-off-by: Rob Murray <rob.murray@docker.com>
