ehea: Merge swqe2 TSO and non TSO paths

write_swqe2_TSO and write_swqe2_nonTSO are almost identical.

For TSO we have to set the TSO and mss bits in the wqe and we only
put the header in the immediate area, no data. Collapse both
functions into write_swqe2_immediate.

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>