[PATCH] include/net/genetlink.h: Allow genlmsg_cancel to accept a NULL argument

nlmsg_cancel can accept NULL as its second argument, so for similarity,
this patch extends genlmsg_cancel to be able to accept a NULL second
argument as well.

Signed-off-by: Julia Lawall <redacted>

---
 include/net/genetlink.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index 8a64b81..b4c7c1c 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h

@@ -195,7 +195,8 @@ static inline int genlmsg_end(struct sk_buff *skb, void *hdr)
  */
 static inline void genlmsg_cancel(struct sk_buff *skb, void *hdr)
 {
-	nlmsg_cancel(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN);
+	if (hdr)
+		nlmsg_cancel(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN);
 }
 
 /**