When a domain has multiple TXT records (SPF, DKIM, etc.), the UDP
response can exceed 512 bytes and the server sets the TC bit. The
verifier was not handling this case, so any truncated response that
omitted the probo-verification record would silently fail as a
mismatch.
Fix by checking resp.Truncated after the UDP exchange and retrying
over TCP when set. Also pass the caller's context instead of
context.Background(), and simplify message construction with
dns.NewMsg.
Closes#1335
Signed-off-by: Bryan Frimin <bryan@probo.com>
95a12d338b