Add handling of LTTNG_ENABLE_EVENT_WITH_EXCLUSION

Add handling of the command LTTNG_ENABLE_EVENT_WITH_EXCLUSION.
The handling of the command is the same as command LTTNG_ENABLE_EVENT,
as the new command is just an extension.

If the command data shows that exclusions and/or filter data will
be following the command structure, read those from the incoming
socket, then forward the filter and exclusion data to
cmd_enable_event().