etherswitchcfg(8): document atu commands

Add documentation for the ATU (Address Translation Unit) commands
that were implemented but not documented in the man page:

- atu dump: display the MAC address table
- atu flush all: clear all dynamic ATU entries
- atu flush port <n>: clear ATU entries for a specific port

Also add atu to the SYNOPSIS section.

PR: 275413
Signed-off-by: Kit Dallege <xaum.io@gmail.com>
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/2096

sbin/etherswitchcfg/etherswitchcfg.8

@@ -22,7 +22,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd June 23, 2021
+.Dd June 9, 2026
 .Dt ETHERSWITCHCFG 8
 .Os
 .Sh NAME
@@ -50,6 +50,10 @@
 .Ar register[=value]
 .Nm
 .Op Fl "f control file"
+.Cm atu
+.Ar command Op Ar parameter
+.Nm
+.Op Fl "f control file"
 .Cm vlangroup%d
 .Ar command parameter
 .Sh DESCRIPTION
@@ -166,6 +170,21 @@ Enable the ingress filter on the port.
 .It Fl ingress
 Disable the ingress filter.
 .El
+.Ss atu
+The atu command provides access to the Address Translation Unit table
+of the switch, which maps MAC addresses to switch ports.
+It supports the following commands:
+.Pp
+.Bl -tag -width ".Cm flush port number" -compact
+.It Cm dump
+Display the current ATU table entries.
+Each entry shows the MAC address and a bitmask of ports associated with it.
+.It Cm flush all
+Remove all dynamic entries from the ATU table.
+.It Cm flush port Ar number
+Remove all dynamic ATU entries associated with port
+.Ar number .
+.El
 .Ss reg
 The reg command provides access to the registers of the switch controller.
 .Ss vlangroup