pyrad 2.2 throws a KeyError exception in DecodePacket if any
attributes from the packet are not defined in the dictionary. Add a
dictionary entry for Service-Type so this doesn't happen.
(cherry picked from commit
e60d01eb1686e112fba4743d4216ba61fec2bdc0)
ticket: 8841
version_fixed: 1.17.1
radius_attributes = '''
ATTRIBUTE User-Name 1 string
ATTRIBUTE User-Password 2 octets
+ATTRIBUTE Service-Type 6 integer
ATTRIBUTE NAS-Identifier 32 string
'''