Add 32 bit ccm test case

[reynir]

I expect this test case to fail on 32 bit architecture due to the following snippet:

mirage-crypto/src/ccm.ml

Lines 54 to 57 in 3ebc0e3

	| x when x < (1 lsl 32) ->
	let buf = Cstruct.create 4 in
	Cstruct.BE.set_uint32 buf 0 (Int32.of_int x) ;
	Cs.of_bytes [0xff ; 0xfe] <+> buf

According to the documentation for lsl the result is unspecified if the right hand side of lsl (in this case 32) is greater than Sys.int_size.

[reynir]

So it did indeed fail, and now I pushed something which I believe will fix it on 32 bit.

[hannesm]

thanks a lot