MFC r318242: Refine and update blacklist support in sshd

Adjust notification points slightly to catch all auth failures, rather
than just the ones caused by bad usernames. Modify notification point
for bad usernames to send new type of BLACKLIST_BAD_USER. (Support in
libblacklist will be forthcoming soon.) Add guards to allow library
headers to expose the enum of action values.

Reviewed by: des
Relnotes: yes
Sponsored by: The FreeBSD Foundation

MFC r305065: Add refactored blacklist support to sshd

Change the calls to of blacklist_init() and blacklist_notify to be
macros defined in the blacklist_client.h file. This avoids
the need for #ifdef USE_BLACKLIST / #endif except in the
blacklist.c file.

Remove redundent initialization attempts from within
blacklist_notify - everything always goes through
blacklistd_init().

Added UseBlacklist option to sshd, which defaults to off.
To enable the functionality, use '-o UseBlacklist=yes' on
the command line, or uncomment in the sshd_config file.

Approved by: des
Sponsored by: The FreeBSD Foundation