net-mgmt/smokeping: fix mail loop issue

Integrate upstream patch[1] to fix mail loop issue #183[2].

This is a one-line patch without complexity who can be removed
as soon as the upstream releases a new version.

[1] https://github.com/oetiker/SmokePing/commit/e9004e8bbeb30d33778afaf70a5f8b95ff38d6ba
[2] https://github.com/oetiker/SmokePing/issues/183

PR: 253161
Submitted by: OlivierW <olivierw1+bugzilla-freebsd@hotmail.com>