ctl.conf(5): fix LUN size in UCL format example.

Remove quotes around size in the LUN section and change the suffix to 'GB'. The
UCL format does recognize 'G' on its own, which uses a base 10 multiplier where
'GB' uses a 2 power multiplier.

Document the difference between valid suffixes when using ctl.conf(5) in the
general syntax form or in UCL format.

Reviewed by:    kevans, mav
Approved by:    kevans (mentor)
Differential Revision: https://reviews.freebsd.org/D26716

usr.sbin/ctld/ctl.conf.5

@@ -28,7 +28,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd July 21, 2016
+.Dd October 13, 2020
 .Dt CTL.CONF 5
 .Os
 .Sh NAME
@@ -426,7 +426,12 @@ property set.
 .It Ic serial Ar string
 The SCSI serial number presented to the initiator.
 .It Ic size Ar size
-The LUN size, in bytes.
+The LUN size, in bytes or by number with a suffix of
+.Sy K , M , G , T
+(for kilobytes, megabytes, gigabytes, or terabytes).
+When the configuration is in UCL format, use the suffix format
+.Sy kKmMgG Ns | Ns Sy bB ,
+(i.e., 4GB, 4gb, and 4Gb are all equivalent).
 .El
 .Sh FILES
 .Bl -tag -width ".Pa /etc/ctl.conf" -compact
@@ -536,7 +541,7 @@ lun {
 	example_0 {
 		path = /dev/zvol/tank/example_0
 		blocksize = 4096
-		size = "4G"
+		size = 4GB
 	}
 
 	example_1 {