Revert back mta's ext propogation to queue.
When NOTIFY=SUCCESS and the relay doesn't advertise DSN we generated a DSN
with "relayed" message.

1) Propogate mta's extension capabilities to queue.
2) Based on mta's extension generate a dsn (relayed vs successful).
3) Modify dsn message according to relay's extension capabilities.
Zero out mta_nodsn field initially.
Merge pull request #334 from snimmagadda/mtaext

Relaying to a non-dsn capable server