[Patch] [BZ 14505] Avoid unwanted A lookups on IPV6 only host

[Roland McGrath]

Seems simpler to test "&& req->ai_family == PF_UNSPEC".
Also, you shouldn't call __nss_lookup_function at all when
you're not going to use its result.  So make it:

	      nss_gethostbyname4_r fct4 = NULL;
	      /* comment */
	      if (req->ai_family == PF_UNSPEC)
	        fct4 = __nss_lookup_function (nip, "gethostbyname4_r");
	      if (fct4 != NULL)

Thanks,
Roland