Fix #433: Allow multiple InterfaceDescriptionBlocks with pcapng.Writer

[powerswitch]

Current version only supports one InterfaceDescriptionBlock, but in general it is allowed to have more then one.

This patch extends the interface so you can provide alternatively a sequence of InterfaceDescriptionBlock instances (or anything which is iterable).

This commit was created by the patch provided as ZIP file by René Liebscher as attachment to the issue.

[coveralls]

Coverage increased (+0.01%) to 92.379% when pulling 14386cd24524d09a0d7f98a26e054df62582baeb on powerswitch:fix-#433 into 49c1af0bf863e404af273544eba939d4fc4d453b on kbandla:master.

[brifordwylie]

@powerswitch @rliebscher @obormot So pulling this branch locally, the tests run fine. When I merge master the tests are failing due to the changes pulled in with the merge of #502. So two options: 1) Someone else merges master into this branch and makes sure the test all pass (just run 'tox' at the top level) 2) I'll do it..make a new PR.. and merge...

Also I think I'm going to put some branch protections on master, to avoid stuff like this in future :)

dpkt/pcapng.py::test_writepkt_epb_ts FAILED
dpkt/pcapng.py::test_custom_read_write FAILED

Both tests fail with the same error

dpkt/pcapng.py:376: in __init__
    self._validate_block('idb', idb_, InterfaceDescriptionBlock)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <dpkt.pcapng.Writer object at 0x102f6fd30>, arg_name = 'idb', blk = ('type', 1)
expected_cls = <class 'dpkt.pcapng.InterfaceDescriptionBlock'>

    def _validate_block(self, arg_name, blk, expected_cls):
        """Check a user-defined block for correct type and endianness"""
        if not isinstance(blk, expected_cls):
>           raise ValueError('{0}: expecting class {1}'.format(
                arg_name, expected_cls.__name__))
E           ValueError: idb: expecting class InterfaceDescriptionBlock

dpkt/pcapng.py:397: ValueError

[powerswitch]

Hi @brifordwylie, sorry for the long absence. I'm only capable to work on the project rarely. But now I'm on holidays, so I pick it up again.

I'll merge the latest master onto the branch and run the tox tests again, will fix them and push the changes. Again, sorry for the delay

[brifordwylie]

@powerswitch @rliebscher looks good, thanks a bunch for the contribution... merging now.