[vmxnet3] Add profiling code to exclude time spent in the hypervisor

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[netdevice] Fix erroneous use of free(iobuf) instead of free_iob(iobuf)

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[libc] Add ASSERTED macro to test if any assertion has triggered

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[list] Add sanity checks after list-adding functions

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