[lotest] Allow loopback testing on shared networks

Allow for extraneous packets to be received during loopback testing,
and so permit loopback tests to be performed when ports are connected
to a switch (rather than requiring ports to be directly connected with
a loopback cable).

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[netdevice] Notify upper-layer drivers when RX processing is (un)frozen

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[efi] Avoid accidentally calling main() twice

EFIRC() uses PLATFORM_TO_ERRNO(), which evaluates its argument twice
(and can't trivially use a braced-group expression or an inline
function to avoid this, since it gets used outside of function
context).

The expression "EFIRC(main())" will therefore end up calling main()
twice, which is not the intended behaviour.  Every other instance of
EFIRC() is of the simple form "EFIRC(rc)", so fix by converting this
instance to match.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[efi] Unload our own image before exiting UEFI application

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