netconsole.txt: revision of examples for the receiver of kernel messages
There are at least 4 implementations of netcat with the BSD-based
being the only one that has to be used without the -p switch to
specify the listening port.
Jan Engelhardt suggested to add an example for socat(1).
Signed-off-by: Dirk Gouders <gouders@et.bocholt.fh-gelsenkirchen.de> Signed-off-by: Cong Wang <amwang@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>