Document the various link-level flag for these drivers.

2.2 candidate (after typo police :)

share/man/man4/man4.i386/vx.4

@@ -28,7 +28,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$Id$
+.\"	$Id: vx.4,v 1.4 1997/03/07 02:49:59 jmg Exp $
 .\"
 .Dd January 15, 1996
 .Dt VX 4 i386
@@ -43,7 +43,19 @@ PCI Ethernet device driver
 The
 .Nm vx
 driver provides support for the 3Com 3c590 and 3c595 EtherLink III and Fast
-EtherLink III PCI Ethernet cards in 10 Mbps mode.
+EtherLink III PCI Ethernet cards in 10 Mbps mode.  The medium selection
+can be influenced by the following link flags to the
+.Xr ifconfig 8
+command:
+.Pp
+.Bl -tag -width LINK0X -compact
+.It Em link0
+Use the AUI port.
+.It Em link1
+Use the BNC port.
+.It Em link2
+Use the UTP port.
+.El
 .Sh DIAGNOSTICS
 .Bl -diag
 .It "vx%d: not configured; kernel is built for only %d devices."

share/man/man4/sl.4

@@ -49,6 +49,21 @@ interface allows serial lines to be used as network interfaces using the
 protocol.  The
 .Nm sl
 interface can use Van Jacobson TCP header compression and ICMP filtering.
+This is arranged by using the various link-level flags to the
+.Xr ifconfig 8
+command:
+.Pp
+.Bl -tag -width LINK0X -compact
+.It Em link0
+Enable VJ header compression.
+.It Em link1
+Supress ICMP traffic.
+.It Em link2
+Enable VJ header compression autodetection.  This will turn on the
+.Em link0
+flag as soon as the first VJ-compressed packet has been seen by
+the driver.
+.El
 .Sh DIAGNOSTICS
 .Bl -diag
 .It sl%d: af%d not supported.