Rework value part of name-value pairs

Rework value part of name-value pairs

NWFilters can be provided name-value pairs using the following
XML notation:

      <filterref filter='xyz'>
        <parameter name='PORT' value='80'/>
        <parameter name='VAL' value='abc'/>
      </filterref>

The internal representation currently is so that a name is stored as a
string and the value as well. This patch now addresses the value part of it
and introduces a data structure for storing a value either as a simple
value or as an array for later support of lists.

This patch adjusts all code that was handling the values in hash tables
and makes it use the new data type.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>