[ipv4] Profile transmit and receive datapaths

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[tcp] Profile transmit and receive datapaths

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[http] Profile receive datapath

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[downloader] Profile receive datapath

Signed-off-by: Michael Brown <mcb30@ipxe.org>