netgraph: Enable support for EIM NAT

Enable support for endpoint-independent mapping ("full cone NAT") via
Libalias's UDP NAT.

Reviewed by:    igoro, thj
Differential Revision:  https://reviews.freebsd.org/D46689

share/man/man4/ng_nat.4

@@ -22,7 +22,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd January 24, 2021
+.Dd December 6, 2024
 .Dt NG_NAT 4
 .Os
 .Sh NAME
@@ -74,6 +74,7 @@ struct ng_nat_mode {
 #define NG_NAT_PROXY_ONLY		0x40
 #define NG_NAT_REVERSE			0x80
 #define NG_NAT_UNREGISTERED_CGN		0x100
+#define NG_NAT_UDP_EIM			0x200
 .Ed
 .Pp
 The corresponding libalias flags can be found by replacing the

sys/netgraph/ng_nat.c

@@ -967,6 +967,8 @@ ng_nat_translate_flags(unsigned int x)
 		res |= PKT_ALIAS_REVERSE;
 	if (x & NG_NAT_UNREGISTERED_CGN)
 		res |= PKT_ALIAS_UNREGISTERED_CGN;
+	if (x & NG_NAT_UDP_EIM)
+		res |= PKT_ALIAS_UDP_EIM;
 
 	return (res);
 }

sys/netgraph/ng_nat.h

@@ -53,6 +53,7 @@ struct ng_nat_mode {
 #define NG_NAT_PROXY_ONLY		0x40
 #define NG_NAT_REVERSE			0x80
 #define NG_NAT_UNREGISTERED_CGN		0x100
+#define NG_NAT_UDP_EIM			0x200
 
 #define NG_NAT_DESC_LENGTH	64
 #define NG_NAT_REDIRPROTO_ADDR	(IPPROTO_MAX + 3) 	/* LibAlias' LINK_ADDR, also unused in in.h */