ip_frag: remove remaining IP checkum offload flag

ip_frag: remove remaining IP checkum offload flag

Currently PKT_TX_IP_CKSUM is being set into mbuf->ol_flags during
fragmentation operation implicitly by the library. Because of this,
application is forced to use checksum offload whether it is supported
by platform or not.

Also documentation does not provide any expected value of ol_flags in
returned fragmented mbufs so application will never come to know that which
offloads are enabled. So transmission may be failed for the platforms which
does not support checksum offload.

So removing mentioned flag from the library.

Mentioned change is part of http://patches.dpdk.org/patch/53475.
Changes for reassembly operation is already accepted. This patch set
implements the similar change for fragmentation operation.

Fixes: e29fc44370c2 ("ip_frag: remove IP checkum offload flag")

Signed-off-by: Sunil Kumar Kori <skori@marvell.com>