net: fix aliasing in checksum computation

net: fix aliasing in checksum computation

That means a superfluous cast is removed and aliasing through a uint8_t
pointer is eliminated. NB: The C standard specifies that a unsigned char
pointer may alias while the C standard doesn't include such requirement
for uint8_t pointers.

Also simplified the loop since a modern C compiler can speed up (i.e.
auto-vectorize) it in a similar way. For example, GCC auto-vectorizes it
for Haswell using AVX registers while halving the number of instructions
in the generated code.

Fixes: 6006818cfb26 ("net: new checksum functions")
Fixes: e079655c41fb ("net: fix build with gcc 4.4.7 and strict aliasing")
Cc: stable@dpdk.org
Signed-off-by: Georg Sauthoff <mail@gms.tf>
Reviewed-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>