Merge pull request kubernetes#3631 from sftim/20221019_fix_ipv6_beta_kep_number

KEP-1138: Fix IPv6 beta kep number

Author: k8s-ci-robot

keps/sig-network/506-ipv6/README.md renamed to keps/sig-network/1138-ipv6/README.md

@@ -1,5 +1,5 @@
-title: graduate-ipv6-to-beta
-kep-number: 506
+title: Graduate IPv6 to beta
+kep-number: 1138
 authors:
   - "@aojea"
 owning-sig: sig-network
@@ -20,4 +20,4 @@ replaces:
 superseded-by:
 
 latest-milestone: "0.0"
-stage: "alpha"
+stage: "beta"