Updates a mail user filter.
$session_id, $client_id, $primary_id, $params
Parameters (in $params):mailuser_id (int(11))
rulename (varchar(64))
source (varchar(255))
searchterm (varchar(255))
op (varchar(255))
action (varchar(255))
target (varchar(255))
active (enum('n','y'))
Output:Returns the number of affected rows.