Update rtsock_l3 test after 2fe5a79425c79f7b828acd91da66d97230925fc8

Two of these tests now pass. Looking at Jenkins to find the first commit
where this behaviour changed indicates that
2fe5a79425c79f7b828acd91da66d97230925fc8 is the most likely cause.

Reviewed By: melifaro
Differential Revision: https://reviews.freebsd.org/D28886