[UDP]: Revert udplite and code split.

[UDP]: Revert udplite and code split.

This reverts commit d322dcf1fad8ce551f7df02692cb7b981284e3f4 ("[IPV6]
UDP: Rename IPv6 UDP files."), commit
d8eafc57f3f9e88416b9611e1627032c6bf85e69 ("[IPV4] UDP: Move
IPv4-specific bits to other file.") and commit
2c3ffa50de9fd21c66a0838cee9247663f028435 ("[UDP]: Allow users to
configure UDP-Lite.").

First, udplite is of such small cost, and it is a core protocol just
like TCP and normal UDP are.

We spent enormous amounts of effort to make udplite share as much code
with core UDP as possible.  All of that work is less valuable if we're
just going to slap a config option on udplite support.

It is also causing build failures, as reported on linux-next, showing
that the changeset was not tested very well.  In fact, this is the
second build failure resulting from the udplite change.

Finally, the config options provided was a bool, instead of a modular
option.  Meaning the udplite code does not even get build tested
by allmodconfig builds, and furthermore the user is not presented
with a reasonable modular build option which is particularly needed
by distribution vendors.

Signed-off-by: David S. Miller <davem@davemloft.net>