ping tests: fix for scapy-2.6.0

Scapy 2.6.0 now appears to parse the IPOption during construction, and it then
gets confused at a single-byte option. IP Options typically contain at least a 1
byte type and 1 byte length. Avoid this by just returning the raw bytes, rather
than an IPOption object.

MFC after: 1 week
Reviewed by: Jose Luis Duran <jlduran@gmail.com>
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D47151

(cherry picked from commit 2926c2594249f64fecbbdcb0b0b9a3591931ab04)