Increase "rndc dnssec -status" output size
BUFSIZ (512 bytes on Windows) may not be enough to fit the status of a DNSSEC policy and three DNSSEC keys.
Set the size of the relevant buffer to a hardcoded value of 4096 bytes, which should be enough for most scenarios.
(cherry picked from commit 9347e7db)
Closes #1988 (closed)