svc: Make svc_recv transport neutral

All of the transport field and functions used by svc_recv are now
transport independent. Change the svc_recv function to use the svc_xprt
structure directly instead of the transport specific svc_sock structure.

Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
Acked-by: Neil Brown <neilb@suse.de>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Greg Banks <gnb@sgi.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>