treewide: use get_random_{u8,u16}() when possible, part 2

Rather than truncate a 32-bit value to a 16-bit value or an 8-bit value,
simply use the get_random_{u8,u16}() functions, which are faster than
wasting the additional bytes from a 32-bit value. This was done by hand,
identifying all of the places where one of the random integer functions
was used in a non-32-bit context.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Heiko Carstens <hca@linux.ibm.com> # for s390
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>