ping: tests: Align with Scapy defaults

Align some of pinger() defaults with Scapy to facilitate debugging when
printing packets.

No functional change intended.

Reviewed by: emaste, kp
Approved by: emaste (mentor)
Differential Revision: https://reviews.freebsd.org/D47159

(cherry picked from commit 4859030ef193688153f490915794ae9ab77f012b)