be2net: Refactor wrb_fill_hdr() routine

The WRB header is setup by wrb_fill_hdr() routine. This routine currently
gets some of the WRB params as args and figures out rest of the WRB params
by looking at various fields in skb (like gso, checksum, vlan-tag etc).
All these params could instead be retrieved from the skb into a structure
and passed to this routine. This separates wrb_fill_hdr() to only provide
chip-specific code to fill the WRB. This also makes it simple to support
chips with different WRB formats.

Signed-off-by: Sriharsha Basavapatna <sriharsha.basavapatna@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>