net-mgmt/portmon: link with -lutil for ftime(3) in 15-CURRENT

The symbol ftime has been moved from libcompat to libutil in 15-CURRENT.
Link with -lutil to pick it up. This doesn't hurt on older FreeBSD.

See also: bb421be6c1174fad837973acc5e4a7bade4489db (src)

MFH: 2024Q4
(cherry picked from commit 33df781ed1ebcca1a022a92d9c3080613d537fca)