BUG/MEDIUM: acme: fix stalled renewal when opportunistic DNS check fails
In ACME_INITIAL_RSLV_READY, when the opportunistic DNS propagation check
fails and the code falls back to ACME_CLI_WAIT, ACME_RDY_INITIAL_DNS was
left set in cond_ready. Since the CLI-wait path only ever sets ACME_RDY_CLI
on auth->ready, the readiness check in ACME_CLI_WAIT could never be
satisfied, permanently stalling certificate renewal.
Fix this by stripping ACME_RDY_INITIAL_DNS from cond_ready before falling
back to the regular CLI-wait flow. Also replace the &= with a plain
assignment in the success path to make the intent explicit.