mount.nfs: support netids in v2/v3 version/transport negotiation

mount.nfs: support netids in v2/v3 version/transport negotiation

When rewriting mount options during v2/v3 negotiation, restore the
correct netids, rather than protocol names, in the rewritten protocol
options.  If TI-RPC is not available, the traditional behavior is
preserved.

This patch assumes the kernel can recognize a netid, instead of a
protocol name, as the value of the proto= options.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>