ifconfig.8: Clean up the channel parameter description

MFC after:	2 weeks

sbin/ifconfig/ifconfig.8

@@ -1220,9 +1220,9 @@ Channels range from 1 to 255, but the exact selection available
 depends on the region your adaptor was manufactured for.
 Setting
 the channel to
-.Li any ,
+.Cm any ,
 or
-.Cm -
+.Dq Cm -
 will clear any desired channel and, if the device is marked up,
 force a scan for a channel to operate on.
 Alternatively the frequency, in megahertz, may be specified
@@ -1232,42 +1232,71 @@ When there are several ways to use a channel the channel
 number/frequency may be appended with attributes to clarify.
 For example, if a device is capable of operating on channel 6
 with 802.11n and 802.11g then one can specify that g-only use
-should be used by specifying ``6:g''.
+should be used by specifying
+.Cm 6:g .
 Similarly the channel width can be specified by appending it
-with ``/''; e.g., ``6/40'' specifies a 40MHz wide channel,
-These attributes can be combined as in: ``6:ht/40''.
-The full set of flags specified following a ``:'' are:
-.Cm a
-(802.11a),
-.Cm b
-(802.11b),
-.Cm d
-(Atheros Dynamic Turbo mode),
-.Cm g
-(802.11g),
-.Cm h
-or
+with
+.Dq Cm \&/ ;
+e.g.,
+.Cm 6/40
+specifies a 40MHz wide channel.
+These attributes can be combined as in:
+.Cm 6:ht/40 .
+.Pp
+The full set of flags specified following a
+.Dq Cm \&:
+are:
+.Pp
+.Bl -tag -compact
+.It Cm a
+802.11a
+.It Cm b
+802.11b
+.It Cm d
+Atheros Dynamic Turbo mode
+.It Cm g
+802.11g
+.It Cm h
+Same as
 .Cm n
-(802.11n aka HT),
-.Cm s
-(Atheros Static Turbo mode),
+.It Cm n
+802.11n aka HT
+.It Cm s
+Atheros Static Turbo mode
+.It Cm t
+Atheros Dynamic Turbo mode, or appended to
+.Cm st
 and
-.Cm t
-(Atheros Dynamic Turbo mode, or appended to ``st'' and ``dt'').
-The full set of channel widths following a '/' are:
-.Cm 5
-(5MHz aka quarter-rate channel),
-.Cm 10
-(10MHz aka half-rate channel),
-.Cm 20
-(20MHz mostly for use in specifying ht20),
-and
-.Cm 40
-(40MHz mostly for use in specifying ht40).
+.Cm dt
+.El
+.Pp
+The full set of channel widths following a
+.Cm \&/
+are:
+.Pp
+.Bl -tag -compact
+.It Cm 5
+5MHz aka quarter-rate channel
+.It Cm 10
+10MHz aka half-rate channel
+.It Cm 20
+20MHz mostly for use in specifying
+.Cm ht20
+.It Cm 40
+40MHz mostly for use in specifying
+.Cm ht40
+.El
+.Pp
 In addition,
 a 40MHz HT channel specification may include the location
-of the extension channel by appending ``+'' or ``-'' for above and below,
-respectively; e.g., ``2437:ht/40+'' specifies 40MHz wide HT operation
+of the extension channel by appending
+.Dq Cm \&+
+or
+.Dq Cm \&-
+for above and below,
+respectively; e.g.,
+.Cm 2437:ht/40+
+specifies 40MHz wide HT operation
 with the center channel at frequency 2437 and the extension channel above.
 .It Cm country Ar name
 Set the country code to use in calculating the regulatory constraints