Detect NSEC3 salt collisions

Detect NSEC3 salt collisions

When generating a new salt, compare it with the previous NSEC3
paremeters to ensure the new parameters are different from the
previous ones.

This moves the salt generation call from 'bin/named/*.s' to
'lib/dns/zone.c'. When setting new NSEC3 parameters, you can set a new
function parameter 'resalt' to enforce a new salt to be generated. A
new salt will also be generated if 'salt' is set to NULL.

Logging salt with zone context can now be done with 'dnssec_log',
removing the need for 'dns_nsec3_log_salt'.

(cherry picked from commit 6b5d7357dfb9d695f02dabb510dbe2ea404ba241)