selftests/net: fix bugs in address and port initialization

Address/port initialization should work correctly regardless
of the order in which command line arguments are supplied,
E.g, cfg_port should be used to connect to the remote host
even if it is processed after -D, src/dst address initialization
should not require that [-4|-6] be specified before
the -S or -D args, receiver should be able to bind to *.<cfg_port>

Achieve this by making sure that the address/port structures
are initialized after all command line options are parsed.

Store cfg_port in host-byte order, and use htons()
to set up the sin_port/sin6_port before bind/connect,
so that the network system calls get the correct values
in network-byte order.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>