[IPV6]: small cleanups

This patch contains the following cleanups:
- addrconf.c: make addrconf_dad_stop() static
- inet6_connection_sock.c should #include <net/inet6_connection_sock.h>
  for getting the prototypes of it's global functions

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: David S. Miller <davem@davemloft.net>