netstat: fix reporting of delivered UDP packets

The counter udps_noport includes udps_noportbcast, so don't subtract
udps_noportbcast twice.

PR: 288680
Reviewed by: rrs
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D51870

(cherry picked from commit d3f2d49e01a867e19186a1db095a7dd66e6c77c0)