bnx2: Update firmware and version

Update 5709 mips firmware to 6.2.1a to fix iSCSI performance
regression.  There was an unnecessary context read in the fast path
affecting performance.

Update bnx2 to 2.1.6.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>