Handle out-of-memory case in svc_tcp.c/svc_unix.c:rendezvous_request.

Handle out-of-memory case in svc_tcp.c/svc_unix.c:rendezvous_request.

If glibc is build with -O3 on at least 390 (-m31) or x86 (-m32),
gcc 11 dumps this warning:
svc_tcp.c: In function 'rendezvous_request':
svc_tcp.c:274:3: error: 'memcpy' offset [0, 15] is out of the bounds [0, 0] [-Werror=array-bounds]
  274 |   memcpy (&xprt->xp_raddr, &addr, sizeof (addr));
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

In out-of-memory case, if one of the mallocs in makefd_xprt function
returns NULL, a message is dumped, makefd_xprt returns NULL
and the subsequent memcpy would copy to NULL.

Instead of a segfaulting, we delay a bit (see also __svc_accept_failed
and Bug 14889 (CVE-2011-4609) - svc_run() produces high cpu usage when
accept() fails with EMFILE (CVE-2011-4609).

The same applies to svc_unix.c.
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>