src: add comment support for objects

Enables specifying an optional comment when declaring named objects. The
comment is to be specified inside the object's block ({} block)

Relies on libnftnl exporting nftnl_obj_get_data and kernel space support
to store the comments.

For consistency, this patch makes the comment be printed first when
listing objects.

Adds a testcase importing all commented named objects except for secmark,
although it's supported.

Example: Adding a quota with a comment

> add table inet filter
> nft add quota inet filter q { over 1200 bytes \; comment "test_comment"\; }
> list ruleset

table inet filter {
	quota q {
		comment "test_comment"
		over 1200 bytes
	}
}

Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/tests/shell/testcases/optionals/dumps/comments_objects_0.nft b/tests/shell/testcases/optionals/dumps/comments_objects_0.nft
new file mode 100644
index 00000000..b760ced6
--- /dev/null
+++ b/tests/shell/testcases/optionals/dumps/comments_objects_0.nft
@@ -0,0 +1,37 @@
+table ip filter {
+	quota q {
+		comment "test1"
+		over 1200 bytes
+	}
+
+	counter c {
+		comment "test2"
+		packets 0 bytes 0
+	}
+
+	ct helper h {
+		comment "test3"
+		type "sip" protocol tcp
+		l3proto ip
+	}
+
+	ct expectation e {
+		comment "test4"
+		protocol tcp
+		dport 666
+		timeout 100ms
+		size 96
+		l3proto ip
+	}
+
+	limit l {
+		comment "test5"
+		rate 400/hour
+	}
+
+	synproxy s {
+		comment "test6"
+		mss 1460
+		wscale 2
+	}
+}