Fix ADSB Squawk back to decimal

[magicrub]

This commit by @MUSTARDTIGERFPV changed the squawk text to be shown in Hex. I'm not sure why, maybe he knows? I've never seen it expressed as a decimal. Technically it's an octal number but decimal is the normal conversion.

[MUSTARDTIGERFPV]

Hey @magicrub! Unfortunately this change doesn't match normal aeronautical standards. A quick check shows squawk values with 5 digit decimal representations. When squawk values are shown for display in applications, they're actually a representation of the octal value as a 4-digit hex value, not as a decimal number.

Take as an example, N635ND flying over the Seattle area right now. They're squawking 1200, the standard US squawk code for VFR flight. Here's that displayed by tar1090.

This matches how a squawk value is entered into a transponder and read over the radio.

By comparison, with your change, now Mission Planner shows this squawk code as 4608. Excuse the weird font, I'm running on macOS because that's what I have available at the moment.

This PR should be reverted.