Make it possible to use alternative source hardware address in the ARP datagram generated by arprequest(). If caller doesn't supply the address, then it is either picked from CARP or hardware address of the interface is taken.
Make it possible to use alternative source hardware address
in the ARP datagram generated by arprequest(). If caller doesn't
supply the address, then it is either picked from CARP or hardware
address of the interface is taken.

While here, make several minor fixes:

- Hold IF_ADDR_RLOCK(ifp) while traversing address list.
- Remove not true comment.
- Access internet address and mask via in_ifaddr fields,
  rather than ifaddr.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase