checkpatch: net and drivers/net: warn on missing blank line after variable declaration

Networking prefers this style, so warn when it's not used.

Networking uses:

    void foo(int bar)
    {
        int baz;

        code...
   }

not

    void foo(int bar)
    {
        int baz;
        code...
    }

There are a limited number of false positives when using macros to
declare variables like:

  WARNING: networking uses a blank line after declarations
  #330: FILE: net/ipv4/inet_hashtables.c:330:
  +	int dif = sk->sk_bound_dev_if;
  +	INET_ADDR_COOKIE(acookie, saddr, daddr)

Signed-off-by: Joe Perches <joe@perches.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>