test_files: Test decoder also with ff-padded input

It's customary in the SIM card universe to right-pad data with ff bytes.
So far we only test decoders without such padding, which is unrealistic.
Let's also tests the decoders with extra 'ff' padding present.

For some files this doesn't make sense, so we add a _test_no_pad class
attribute that can be spcified to prevent this new "test with ff-padding"
from being executed for the test data of the class.

Change-Id: I7f5cbb4a6f91040fe9adef9da0a1f30f9f156dae

pySim/ts_31_102.py

@@ -526,6 +526,7 @@ class EF_ECC(LinFixedEF):
                                               "marine_guard": False, "mountain_rescue": False,
                                               "manual_ecall": False, "automatic_ecall": False } } ),
     ]
+    _test_no_pad = True
     cc_construct = BcdAdapter(Rpad(Bytes(3)))
     category_construct = FlagsEnum(Byte, police=1, ambulance=2, fire_brigade=3, marine_guard=4,
                                    mountain_rescue=5, manual_ecall=6, automatic_ecall=7)
@@ -588,6 +589,8 @@ class EF_AD(TransparentEF):
                                              "prose_services": False, "extended_drx": False },
                         "rfu": 0, "mnc_len": 2, "extensions": b'' } ),
     ]
+    _test_no_pad = True
+
     class OP_MODE(enum.IntEnum):
         normal = 0x00
         type_approval = 0x80