audit: tidy and extend netfilter_cfg x_tables

audit: tidy and extend netfilter_cfg x_tables

NETFILTER_CFG record generation was inconsistent for x_tables and
ebtables configuration changes.  The call was needlessly messy and there
were supporting records missing at times while they were produced when
not requested.  Simplify the logging call into a new audit_log_nfcfg
call.  Honour the audit_enabled setting while more consistently
recording information including supporting records by tidying up dummy
checks.

Add an op= field that indicates the operation being performed (register
or replace).

Here is the enhanced sample record:
  type=NETFILTER_CFG msg=audit(1580905834.919:82970): table=filter family=2 entries=83 op=replace

Generate audit NETFILTER_CFG records on ebtables table registration.
Previously this was being done for x_tables registration and replacement
operations and ebtables table replacement only.

See: https://github.com/linux-audit/audit-kernel/issues/25
See: https://github.com/linux-audit/audit-kernel/issues/35
See: https://github.com/linux-audit/audit-kernel/issues/43

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>