Lua accessor for Protocol field type gets wrong data

When a Lua dissector/tap accesses the value of a Field of FT_PROTOCOL ftype, the
returned ByteArray contains the wrong data.  Also, calling such a field's
tostring() method returns a string of "(unknown)" instead of the hex of the
data.

Bug: 10801
Change-Id: I8a0642dc0e41af444d211bbe4106cd21207084a6
Reviewed-on: https://code.wireshark.org/review/6003
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Hadriel Kaplan <hadrielk@yahoo.com>
Tested-by: Hadriel Kaplan <hadrielk@yahoo.com>