net/core: make sock_diag.c explicitly non-modular

net/core: make sock_diag.c explicitly non-modular

The Makefile currently controlling compilation of this code lists
it under "obj-y" ...meaning that it currently is not being built as
a module by anyone.

Lets remove the modular code that is essentially orphaned, so that
when reading the driver there is no doubt it is builtin-only.

Since module_init translates to device_initcall in the non-modular
case, the init ordering remains unchanged with this commit.  We can
change to one of the other priority initcalls (subsys?) at any later
date, if desired.

We can't remove module.h since the file uses other module related
stuff even though it is not modular itself.

We move the information from the MODULE_LICENSE tag to the top of the
file, since that information is not captured anywhere else.  The
MODULE_ALIAS_NET_PF_PROTO becomes a no-op in the non modular case, so
it is removed.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Craig Gallek <kraig@google.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>