Handle the current message's being aborted.
||xxfi_abort may be called at any time during message processing
(i.e. between some message-oriented routine and xxfi_eom).
||Do nothing; return SMFIS_CONTINUE.
||Opaque context structure.
- xxfi_abort must reclaim any resources allocated on a
per-message basis, and must be tolerant of being called between any
two message-oriented callbacks.
- Calls to xxfi_abort and xxfi_eom
are mutually exclusive.
- xxfi_abort is not responsible for reclaiming
connection-specific data, since xxfi_close is always called when a connection
- Since the current message is already being aborted, the return
value is currently ignored.
- xxfi_abort is only called if the message is aborted outside the
filter's control and the filter has not completed its
message-oriented processing. For example, if a filter has already
returned SMFIS_ACCEPT, SMFIS_REJECT, or SMFIS_DISCARD from a
message-oriented routine, xxfi_abort will not be called even if the
message is later aborted outside its control.