Remove skb linearization

[planetA]

Function rxe_udp_encap_recv is responsible for receiving the RoCE packets. For each packet, it linearizes the skb:

linux/drivers/infiniband/sw/rxe/rxe_net.c

Line 205 in ea2cec2

if (skb_linearize(skb)) {

This operation hurts performance a lot and must be removed from the critical path. Unfortunately, it requires non-trivial changes through the whole driver code, as accessing packet becomes less trivial.