backwards compatibility: fix order of fields in TI-RPC's svc_req

backwards compatibility: fix order of fields in TI-RPC's svc_req

Preserve ABI compatibility between glibc's RPC implementation and
the legacy RPC implementation in libtirpc by moving the rq_xprt
field in the TI-RPC version of the svc_req struct so it is
backwards compatible with the legacy version of this structure.

Linux's legacy svc_req struct, from /usr/include/rpc/svc.h, looks
like this:

struct svc_req {
  rpcprog_t rq_prog;		/* service program number */
  rpcvers_t rq_vers;		/* service protocol version */
  rpcproc_t rq_proc;		/* the desired procedure */
  struct opaque_auth rq_cred;	/* raw creds from the wire */
  caddr_t rq_clntcred;		/* read only cooked cred */
  SVCXPRT *rq_xprt;		/* associated transport */
};

The new TI-RPC svc_req struct, from /usr/include/tirpc/rpc/svc.h,
looks like this:

struct svc_req {
  u_int32_t rq_prog;		/* service program number */
  u_int32_t rq_vers;		/* service protocol version */
  u_int32_t rq_proc;		/* the desired procedure */
  struct opaque_auth rq_cred;	/* raw creds from the wire */
  void *rq_clntcred;		/* read only cooked cred */
  caddr_t rq_clntname;		/* read only client name */
  caddr_t rq_svcname;		/* read only cooked service cred */
  SVCXPRT *rq_xprt;		/* associated transport */
};

Note the extra fields rq_clntname and rq_svcname.  These are used for
TI-RPC's RPCSEC GSS flavor support.

This issue came to light because rpc.statd still uses only legacy RPC
calls, and thus includes /usr/include/rpc/svc.h.  However, other parts
of nfs-utils now link with TI-RPC, so the legacy RPC functions in
libtirpc are used in favor of glibc's RPC functions.  The libtirpc svc
functions use the new svc_req struct, but rpc.statd uses the old
svc_req struct.

Since the svc_req fields were different, rpc.statd broke after recent
IPv6-related changes, even though I hadn't made any changes to it.
Note that rpc.mountd also references the rq_xprt field, so it has the
same issue.

In most operating systems, there is only one rpc/svc.h and one version
of svc_req so this is not a problem.  We should audit all of the
structures and functions under /usr/include/rpc and
/usr/include/tirpc/rpc to ensure we have a reasonable level of
backwards compatibility until such a time it is decided to merge these
implementations or get rid of RPC support in glibc.

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