[PATCH nft] evaluate: suggest != in negation error message

[Florian Westphal <fw@strlen.de>]

  when I run sudo nft insert rule filter FORWARD iifname "ens2f1" ip saddr not @ip_macs counter drop comment \" BLOCK ALL NON REGISTERED IP/MACS \"
  I get: Error: negation can only be used with singleton bitmask values

And even I did not spot the problem immediately.

I don't think "not" should have been added, its easily confused with
"not equal"/"neq"/!= and hides that this is (allegedly) a bit operation.

At least suggest to use != instead in the error message, I suspect it
might lessen the pain.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/evaluate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/evaluate.c b/src/evaluate.c
index c699a9bc7b86..b7ae9113b5a8 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -2480,7 +2480,7 @@ static int expr_evaluate_relational(struct eval_ctx *ctx, struct expr **expr)
 			    right->dtype->basetype == NULL ||
 			    right->dtype->basetype->type != TYPE_BITMASK)
 				return expr_binary_error(ctx->msgs, left, right,
-							 "negation can only be used with singleton bitmask values");
+							 "negation can only be used with singleton bitmask values.  Did you mean \"!=\"?");
 		}
 
 		switch (right->etype) {
-- 
2.41.0