split is_immune into itself + is_naughty
split is_immune into itself + is_naughty

is_immune tests designates to plugins they should always skip processing.

That's typical for naughty connections, but this change provides the ability to handly naughty connections differently than (whitelisted/relayclients/known good) senders.

sieutruc/qpsmtpd,salvis/qpsmtpd,priyadi/qpsmtpd,priyadi/qpsmtpd,smtpd/qpsmtpd,smtpd/qpsmtpd,msimerson/qpsmtpd,priyadi/qpsmtpd,sieutruc/qpsmtpd,sentinelleader/qpsmtpd-dev,sieutruc/qpsmtpd,salvis/qpsmtpd,sentinelleader/qpsmtpd-dev,msimerson/qpsmtpd