selftests: netfilter: nft_meta.sh: small shellcheck cleanup

shellcheck complains about missing "", so add those.
Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20240418152744.15105-11-fw@strlen.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/netfilter/nft_meta.sh

@@ -91,10 +91,10 @@ check_one_counter()
 	local want="packets $2"
 	local verbose="$3"
 
-	if ! ip netns exec "$ns0" nft list counter inet filter $cname | grep -q "$want"; then
+	if ! ip netns exec "$ns0" nft list counter inet filter "$cname" | grep -q "$want"; then
 		echo "FAIL: $cname, want \"$want\", got"
 		ret=1
-		ip netns exec "$ns0" nft list counter inet filter $cname
+		ip netns exec "$ns0" nft list counter inet filter "$cname"
 	fi
 }