bridge: Use %D identifier to format MAC address

[zlei]

Summary

It is shorter and more readable.

No functional change intended.

Fixes: 2d3614fb132b bridge: Log MAC address port flapping
MFC after: 8 days

[kp]

I did not know about %D. It's good to learn things :)

[zlei]

In D39542#900188, @kp wrote:

I did not know about %D. It's good to learn things :)

I found that while hacking the VLAN PCP bugs ;)

See sys/net/if_ethersubr.c:

/*
 * Perform common duties while attaching to interface list
 */
void
ether_ifattach(struct ifnet *ifp, const u_int8_t *lla)
{
...
        if (i != ifp->if_addrlen)
                if_printf(ifp, "Ethernet address: %6D\n", lla, ":");
...
}