Increase initial size of usb_string_serial_number by 2 on Teensy3/Teensy4

[hmaarrfk]

I was auditing the code and noticed two things:

1. The initial size is 12, which is: not equal to 10 * 2, 0, or 10
2. The data is copied from a buffer of size 11, so the size should be at least 11.

I am unsure if the default value should be bLength=24 or bLength=2, both seem somewhat valid to me.

[PaulStoffregen]

This is incorrect. Please read the USB 2.0 spec regarding string descriptors.

[hmaarrfk]

Will reopen. thank you.

[hmaarrfk]

I see, i read that it is in fact 2 + "length of string". The string stored is not "null terminated".

I still think that the value of "12" is off. it should be either "2" or "22" as I understand it.

[hmaarrfk]

ultimately, it is inconsequential due to the initialization routine. thanks for the usb pointer.

[PaulStoffregen]

I still think that the value of "12" is off. it should be either "2" or "22" as I understand it.

[PaulStoffregen]

Oh, yes, now I see. It should be 22. If you still care about this, please send a new PR which just changes 12 to 22.