staging: ramster: depend on NET for sock_* functions

Building ramster without NET would cause linkage issue due to missing
sock_*() functions in cluster/tcp.c

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>