Expand the Advanced Networking page to all options

For issue #5658 this rewrite of the networking page explains what every
single option (unless I missed one!) does both for the Docker server and
also the Docker client when submitting a "docker run".  I somehow
thought that, when I was done, there would be a lot more about setting
up topologies like I did for my Foundations of Python Network
Programming network of Docker containers.  More about making routers and
firewalls that NAT and so forth.  But, at least for this draft, I think
that setting up subnets and setting up point-to-point links is most of
what Docker users will need unless they are doing something exotic.

We can always expand later.

Docker-DCO-1.1-Signed-off-by: Brandon Rhodes <brandon@rhodesmill.org> (github: brandon-rhodes)

Improve networking.md documentation per @jamtur01

Besides catching some typos and awkward sentences, @jamtur01 had several
more thorough changes to suggest:

 *  He illustrated the correct way to delimit "Note" paragraphs in
     Docker documentation.

 *  He helped point out where I was presuming an Ubuntu host running
    Docker, so that I could re-word those sections to be specific that
    the advice only applied to Ubuntu (these mostly related to how to
    set server-wide options and restart the server).

 *  He is happy to have "Ethernet" capitalized even where Linux
    documentation would render it with an ugly lower-case first letter.

Docker-DCO-1.1-Signed-off-by: Brandon Rhodes <brandon@rhodesmill.org> (github: brandon-rhodes)

Improve networking.md per ideas from @SvenDowideit

A response to a bit of further discussion of pull request #5884.