The upgrade to libdialog 1.3 included changes to the ABI.
Bump libdpv to 3 since it links against libdialog.
Reported by: Mark Millard <marklmi@yahoo.com>
Reviewed by: bapt
Fixes: a96ef45019 dialog: import dialog 1.3-20210117
Differential Revision: https://reviews.freebsd.org/D32675