bnx2x: allocate memory dynamically in ethtool self-test.

From: Merav Sicron <meravs@broadcom.com>

Current ethtool self tests usesa large buffer on stack. This patch replaces
that array by dynamically allocated memory

Signed-off-by: Merav Sicron <meravs@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>