While functionally compatible with the implementation in ElementalIRCd, our approach is different,
specifically pre-calculating the bitmask at config load time. This is more efficient, and allows us
to report errors as part of the configuration phase.
This allows multiple improvements to m_sasl. With this change, the SASL
authentication gets aborted immediately when services are offline.
Additionally, we send the SASL ENCAP messages directly to the specified
SASL agent.
There are IPv4 and IPv6 ranges reserved for documentation and example code;
use these to minimize the risk if someone accidentally uses an unmodified
example conf.