Fixed wrong type in serial CRC function

[hairymnstr]

The CRC function was calculating the wrong CRC due to a regression in the variable type.

[cguimaraes]

Is this introducing any any warning or error in your setup / scenario?
This change of type was intentionally introduced by the Windows port.

[hairymnstr]

Without this fix I get CRC errors when talking to zenohd over the serial transport:

[2023-03-21T07:48:37Z ERROR zenoh_link_serial::unicast] Read error on Serial link serial//dev/ttyACM0 => serial/f7c0887d-f068-4ba2-910a-b2e7deb108ee: CRC does not match Received 54CF142 Computed F82CABD3 at io/zenoh-links/zenoh-link-serial/src/unicast.rs:150.

[cguimaraes]

Let me take a look then.
I want to avoid warnings on Windows as well before merging it.

In the meantime, in order to be able to accept any PR, you need to sign the Eclipse Contributor Agreement. Click on the failing test to see how.

[cguimaraes]

@hairymnstr I pushed two commits on top of your PR.
Can you double check that everything still works on your side?

Upon validation, as well as a valid ECA on your side, we will be able to merge your contribution.

[hairymnstr]

I've tested the code with your commits and it's working for me.

The bit with the issue was (crc >> 1) which is an arithmetic shift (i.e. sign extends in signed types).

[cguimaraes]

Fixes #177 .

[cguimaraes]

LGTM