[NetLabel]: consolidate the struct socket/sock handling to just struct sock

The current NetLabel code has some redundant APIs which allow both
"struct socket" and "struct sock" types to be used; this may have made
sense at some point but it is wasteful now.  Remove the functions that
operate on sockets and convert the callers.  Not only does this make
the code smaller and more consistent but it pushes the locking burden
up to the caller which can be more intelligent about the locks.  Also,
perform the same conversion (socket to sock) on the SELinux/NetLabel
glue code where it make sense.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: David S. Miller <davem@davemloft.net>