[NETFILTER]: ctnetlink: rework conntrack fields dumping logic on events

               |   NEW   | UPDATE  | DESTROY |
     ----------------------------------------|
     tuples    |    Y    |    Y    |    Y    |
     status    |    Y    |    Y    |    N    |
     timeout   |    Y    |    Y    |    N    |
     protoinfo |    S    |    S    |    N    |
     helper    |    S    |    S    |    N    |
     mark      |    S    |    S    |    N    |
     counters  |    F    |    F    |    Y    |

 Leyend:
         Y: yes
         N: no
         S: iif the field is set
	 F: iif overflow

This patch also replace IPCT_HELPINFO by IPCT_HELPER since we want to
track the helper assignation process, not the changes in the private
information held by the helper.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>