MINOR: checks: Add support to set-var and unset-var rules in tcp-checks

MINOR: checks: Add support to set-var and unset-var rules in tcp-checks

Evaluate the registered action_ptr associated with each CHK_ACTION_KW rules from
a ruleset. Currently only the 'set-var' and 'unset-var' are parsed by the
tcp-check parser. Thus it is now possible to set or unset variables. It is
possible to use such rules before the first connect of the ruleset.