eapmd5tojohn.c: Endianness swapping macros may clash with Linux kernel's

[solardiz]

As seen in warnings in the screenshot in #5109, the __swab* macros in our eapmd5tojohn.c may clash with same-named macros in the Linux kernel's headers. Somehow this does not happen on typical Linux systems, but apparently it did under termux on Android?

We should probably change eapmd5tojohn.c to use our shared JOHNSWAP* macros, like e.g. wpapcap2john.h already does. BTW, we don't have a 16-bit byte swap macro (we only have 32- and 64-bit) - maybe we need to add one, not to duplicate that primitive across files.