Wrong parameter when initializing with data file

[nwhitehair]

When a SigMFFile object is created with a pre-exisiting data file, the skip_checksum argument is passed in the wrong position to the set_data_file method. This incorrectly sets the value of the data_buffer parameter instead and causes skip_checksum to always take its default value when initializing with data.

PR #9 fixes the problem by passing skip_checksum by name instead of by position.

[Netherdrake]

I get the same error on collection.get_SigMFFile with sigmf = {editable = true, ref = "initialization-bugfix", git = "https://github.com/nwhitehair/sigmf-python"} as well

[nwhitehair]

@Netherdrake Can you clarify what problem you're seeing? I haven't worked with SigMFCollection much, but everything looks correct as far as I can tell when I create an instance from some recordings I have.