This fixes the following bug: When scanning with an Ethernet handle (as
opposed to raw sockets), only the first host in an OS scan group would
get a result. All others would be blank fingerprints with R=N for every
probe. This was first noticed on Windows because Ethernet is the default
sending method, but it affects other platforms with --send-eth.
OS scan initialized an Ethernet handle once for each group, and recorded
the first-hop MAC address of the first target at that time. That
first-hop address was used for all targets. This failed on a switched
LAN, when the first-hop address for every host is different (it's the
MAC address of each target).
All the various high-level probe sending functions now do their work
through three low-level sending functions: one each for TCP, UDP, and
ICMP. Those low-level functions take care of setting the MAC addresses
before each send.
I checked and the other places where Ethernet sends are used do not have
this problem. ultra_scan, idle scan, and traceroute all set the
addresses before every send.
