Use separate IFCAPs for LRO and TSO.

Use separate IFCAPs for LRO and TSO.

This diff introduces separate capabilities for TCP offloading.  We split this
into LRO (large receive offloading) and TSO (TCP segmentation offloading).
LRO can be turned on/off via tcprecvoffload option of ifconfig and is not
inherited to sub interfaces.

TSO is inherited by sub interfaces to signal this hardware offloading capability
to the network stack.

With tweaks from bluhm, claudio and dlg

ok bluhm, claudio