freetdm/libpri: Add support to change status of an individual channel or multiple channel.  This allow to put bchannel out of service on an active T1 without affecting active call.  Allow graceful out of service of T1 trunk.
NOTE: There is bugs in libpri, even latest 1.4.12 as of this writing if you use NI2.   So rightnow it only work in DMS100/ATT mode.  Email me to get the NI2 patch (really stupid error).
NOTE2: The way libpri is build doesn't allow to do advance feature with the SERVICE feature, so if you put an channel out of service, and the far end send an restart, it will be bring back in service.  Lot of changes in libpri is required to allow this.  I need to figure out what would be the best steps to take since I don't have commit access to libpri release.
NOTE3: You need to enable this feature by setting service_message_support to true on the span