tests: python3 use byte strings in raw()

tests: python3 use byte strings in raw()

Raw('\xaf) and Raw(b'\xaf) are two quite different things in python 2 versus 3.
In most cases this didn't make a difference, apart from those cases where length
of payload actually mattered.

Type: fix
Signed-off-by: Ole Troan <ot@cisco.com>
Change-Id: I3cba5c1486e436a3ca8aa10a7b393da75aa9f6b9