Multi-Exit Discriminator Selector. This parameter
indicates whether or not a MULTI_EXIT_DISC will be
advertised for a network matching this filter and, if
advertised, what value to use. 'none' indicates that no
value will be advertised. 'specified' indicates that
the value in wfIpBgp4AnnounceMultiExitDisc will be used.
'originating' indicates that the metric from the
originating protocol will be used. Only valid if
'action' is 'announce'.