Allow channel number in hexa in cli argument

[fredericgermain]

As title says, allow giving channel with hexadecimal notation

Example :

./whsniff -c 0xb

is the same as

./whsniff -c 11

[homewsn]

Thank you. I think this will be useful. But your code converts, for example, dxb to 13.

[fredericgermain]

Hi!

I pushed a new commit that improve the parsing, and handle the dxb case.

[homewsn]

Ok. Thanks.