helper : Fix UDP checksum computation
helper : Fix UDP checksum computation

This patch fixes the following problems:
- checksum computation for LE platforms
- checksum is computed in the CPU endianness. The returned result
must be converted to the BE ordering when it is used to update the
UDP checksum in a packet.
- checksum computation for packets having the UDP length not a
multiple of 2.

Signed-off-by: Grigore Ion <8ee9d4b314276fac42961f68b856935d621ac12b@freescale.com>
Reviewed-by: Bill Fischofer <52f3c909d51cc5d355a68a403df6906b3c1a8f83@linaro.org>
Signed-off-by: Maxim Uvarov <db4d16e02ae2d7493db430203537da8b2e34f290@linaro.org>

kalray/odp-mppa,rsalveti/odp,kalray/odp-mppa,ravineet-singh/odp,mike-holmes-linaro/odp,nmorey/odp,kalray/odp-mppa,rsalveti/odp,dkrot/odp,erachmi/odp,erachmi/odp,ravineet-singh/odp,mike-holmes-linaro/odp,mike-holmes-linaro/odp,kalray/odp-mppa,dkrot/odp,dkrot/odp,dkrot/odp,rsalveti/odp,kalray/odp-mppa,rsalveti/odp,ravineet-singh/odp,rsalveti/odp,erachmi/odp,nmorey/odp,kalray/odp-mppa,mike-holmes-linaro/odp,ravineet-singh/odp,kalray/odp-mppa,nmorey/odp,nmorey/odp,erachmi/odp