bnx2x: Re-factor Tx code

Add support for IPv6 TSO
Re-factor the Tx code with smaller functions to increase readability.
Add linearization code in case packet is too fragmented for the
microcode to handle.

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