Does anyone know why you would use an unsigned char array to store the MAC address instead of uint8_t? Char is one byte but a but a byte is not guaranteed to be 8 bits yet MAC is defined as 48 bits
That said, since the next field is a uint16_t, you may as well stay in Rome and call them uint8_t. short really is variable on some live architectures.
(Ok, or some DSPs only address words larger than 8 bits, but there's no reason for your compiler not to pick up the slack.)
Also, TIL that __attribute__((packed)) assumes the struct can be malevolently aligned and for some architectures generates very large and slow code to handle that. If you must pack, also add the ",aligned(2)" or whatever you can get away with to mitigate this.
TI's C2000 microcontrollers - a byte is 16 bits. Other TI DSPs also have 16 bit bytes.
Of course, "int" is less typing than "int_fast16_t". But, int_fast16_t possibly makes it more obvious why you've chosen the type you did (i.e. you only need 16-bits, but aren't relying on any overflow so a bigger type can freely be substituted if that gives better performance.)
But you're right - if uint8_t exists, it must be the same as unsigned char.