Fix dhcp4 mac address retrieve method

[schenot]

The getMAC method of pkt4 seems to retrieve the mac of the packet sender which is not the client MAC if a dhcp-relay is used.

The getHWAddr seems to be the method used in the KEA server (it's used in src/bin/dhcp4/dhcp4_srv.cc of the KEA 1.6.1 sources) and return the expected MAC address.

I test this patch with KEA 1.6.1 sources and hook release v1.3.1, it work as expected. Without this path the MAC address in KEA_QUERY4_HWADDR is the MAC address of my default gateway, because the packet is forwarded from a dhcp-relay.

[zorun]

Hmm, strange, I would have said it works the other way around:

• getHWAddr() just returns an attribute: https://jenkins.isc.org/job/Kea_doc/doxygen/dd/d08/pkt4_8h_source.html#l00326
• getMAC() does much more work and is able to look at options inserted by relays: https://jenkins.isc.org/job/Kea_doc/doxygen/d7/d84/pkt_8cc_source.html#l00146 (although looking at it again, it's obvious that it starts with the MAC address of raw socket)

But since I haven't actually tested it with a relay and you have, I'm going to trust you and merge this!

[zorun]

Merged and released as 1.3.2, thanks!