ethernet/broadcom: use core min/max MTU checking

ethernet/broadcom: use core min/max MTU checking

tg3: min_mtu 60, max_mtu 9000/1500

bnxt: min_mtu 60, max_mtu 9000

bnx2x: min_mtu 46, max_mtu 9600
- Fix up ETH_OVREHEAD -> ETH_OVERHEAD while we're in here, remove
  duplicated defines from bnx2x_link.c.

bnx2: min_mtu 46, max_mtu 9000
- Use more standard ETH_* defines while we're at it.

bcm63xx_enet: min_mtu 46, max_mtu 2028
- compute_hw_mtu was made largely pointless, and thus merged back into
  bcm_enet_change_mtu.

b44: min_mtu 60, max_mtu 1500

CC: netdev@vger.kernel.org
CC: Michael Chan <michael.chan@broadcom.com>
CC: Sony Chacko <sony.chacko@qlogic.com>
CC: Ariel Elior <ariel.elior@qlogic.com>
CC: Dept-HSGLinuxNICDev@qlogic.com
CC: Siva Reddy Kallam <siva.kallam@broadcom.com>
CC: Prashant Sreedharan <prashant@broadcom.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>