cifs: make sure we allocate enough storage for socket address

The sockaddr declared on the stack in cifs_get_tcp_session is too small
for IPv6 addresses. Change it from "struct sockaddr" to "struct
sockaddr_storage" to prevent stack corruption when IPv6 is used.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>