* common/dns-cert.c: Remove iobuf.h.
(get_dns_cert): Rename to _get_dns_cert.  Remove MAX_SIZE arg.  Change
iobuf arg to a estream-t.  Rewrite function to make use of estream
instead of iobuf.  Require all parameters.  Return an gpg_error_t
error instead of the type.  Add arg ERRSOURCE.
* common/dns-cert.h (get_dns_cert): New macro to pass the error source
to _gpg_dns_cert.
* common/t-dns-cert.c (main): Adjust for changes in get_dns_cert.
* g10/keyserver.c (keyserver_import_cert): Ditto.
* doc/gpg.texi (GPG Configuration Options): Remove max-cert-size.