qed: Add ll2 option to limit the number of bds per packet

iWARP uses 3 ll2 connections, the maximum number of bds is known
during connection setup. This patch modifies the static array in
the ll2_tx_packet descriptor to be a flexible array and
significantlly reduces memory size.

In addition, some redundant fields in the ll2_tx_packet were
removed, which also contributed to decreasing the descriptor size.

Signed-off-by: Michal Kalderon <Michal.Kalderon@cavium.com>
Signed-off-by: Ariel Elior <Ariel.Elior@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>