9p: restrict RDMA usage

Make 9p's RDMA option depend on INET since it uses Infiniband rdma_*
functions and that code depends on INET.  Otherwise 9p can try to
use symbols which don't exist.

ERROR: "rdma_destroy_id" [net/9p/9pnet_rdma.ko] undefined!
ERROR: "rdma_connect" [net/9p/9pnet_rdma.ko] undefined!
ERROR: "rdma_create_id" [net/9p/9pnet_rdma.ko] undefined!
ERROR: "rdma_create_qp" [net/9p/9pnet_rdma.ko] undefined!
ERROR: "rdma_resolve_route" [net/9p/9pnet_rdma.ko] undefined!
ERROR: "rdma_disconnect" [net/9p/9pnet_rdma.ko] undefined!
ERROR: "rdma_resolve_addr" [net/9p/9pnet_rdma.ko] undefined!

I used an if/endif block so that the menu items would remain
presented together.

Also correct an article adjective.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>