DHCP fixes #548
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DHCP fixes #548
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This fixes DHCP on Linksys WRT1900AC. With 0x0001, it would not reply to DISCOVERs at all, probably because seeing an unknown reserved flag being set. With 0x8000, it works fine.
Reasons:
1. We were already accidentally not setting the BROADCAST flag due to it being the wrong bit (see previous commit).
2. Major OSes don't set it.
3. rfc1542 section 3.1.1 states it's discouraged, and the issue it's supposed to workaround doesn't apply to smoltcp.
Unfortunately, some client implementations are
unable to receive such unicast IP datagrams until they know their own
IP address
(..)
This addition to the protocol is a workaround for old host
implementations. Such implementations SHOULD be modified so
that they may receive unicast BOOTREPLY messages, thus making
use of this workaround unnecessary. In general, the use of
this mechanism is discouraged.
This is a minor security improvement against blind packet spoofing, since it adds more entropy to the packets.
This workarounds a known broken Vodafone Fiber router which replies with both NAK and ACK: 
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bors r+ |
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Several fixes, including one that fixes DHCP not working with some routers.
See individual commit messages for details.