Another improvement to create_netmail():

If the SMB header contains a source FTN address, use that as the origin address
of the netmail and do not look-up a local AKA match for the destination address.
Also, fix what appears to have been a (currently harmless) bug in
smsg_to_echostat_msg(): the msg.from_net.addr is not an ASCIIZ string when
net.type == NET_FIDO. Currently, source FTN addresses aren't set in echomail
message headers, where the echostats come from. Could just remove
these 2 lines.