[NFS] Set CONFIG_KEYS when CONFIG_NFS_USE_KERNEL_DNS is set

Previous patch relied on DNS_RESOLVER setting CONFIG_KEYS
but needs to be selected in NFS config when using the new
DNS resolver
Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
CC: David Howells <dhowells@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/nfs/Kconfig

@@ -115,4 +115,5 @@ config NFS_USE_KERNEL_DNS
 	bool
 	depends on NFS_V4 && !NFS_USE_LEGACY_DNS
 	select DNS_RESOLVER
+	select KEYS
 	default y