[dhcp] Check for matching chaddr in received DHCP packets

On large networks a DHCP XID collision is possible.  Fix by explicitly
checking the chaddr in received DHCP packets.

Originally-fixed-by: Wissam Shoukair <wissams@mellanox.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
[dhcp] Remove obsolete dhcp_chaddr() function

As of commit 03f0c23 ("[ipoib] Expose Ethernet-compatible eIPoIB
link-layer addresses and headers"), all link layers have used
addresses which fit within the DHCP chaddr field.  The dhcp_chaddr()
function was therefore made obsolete by this commit, but was
accidentally left present (though unused) in the source code.

Remove the dhcp_chaddr() function and the only remaining use of it,
unnecessarily introduced in commit 08bcc0f ("[dhcp] Check for matching
chaddr in received DHCP packets").

Reported-by: Wissam Shoukair <wissams@mellanox.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
[build] Use -malign-double to build 32-bit UEFI binaries

The EDK2 codebase uses -malign-double for 32-bit builds, which causes
64-bit integers to be naturally aligned.  This affects the layout of
some structures (including EFI_BLOCK_IO_MEDIA).

This mirrors wimboot commit 7b8f39d ("[build] Fix building of 32-bit
UEFI version").

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