ehea: Simplify type 3 transmit routine

If a nonlinear skb fits within the immediate area, use skb_copy_bits
instead of copying the frags by hand.

v3:
[cascardo] fixed conflict with use of skb frag API

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>