The interface was hard coded to wln0 which works when running single
tests but not when running multiple. Instead use the actual ifname
that hostapd is using.
Tests that DHCP using IWD's internal netconfig functions properly.
The actual IP address assignment is not verified, but since IWD does
not signal the connection as successful unless DHCP succeeds we
can assume it was successful by checking that the device is connected.
The process of actually starting dhcpd and configuring the interfaces
is quite simple so it was left in the autotest itself. If (or when)
more tests require IP capabilities (p2p, FILS, etc) this could be
moved into test-runner itself and be made common. The reason I did not
put it in there now is a) because this is the only test and b) more
complex DHCP cases are likely to develop and may require more than this
simplistic setup (like multiple APs/interfaces)
