dracut.cmdline.7.asc: document bond mtu option

dracut.cmdline.7.asc

@@ -569,13 +569,14 @@ interface name. Better name it "bootnet" or "bluesocket".
     VLAN_PLUS_VID_NO_PAD (vlan5), DEV_PLUS_VID (eth0.0005),
     DEV_PLUS_VID_NO_PAD (eth0.5)
 
-**bond=**__<bondname>__[:__<bondslaves>__:[:__<options>__]]::
+**bond=**__<bondname>__[:__<bondslaves>__:[:__<options>__[:<mtu>]]]::
     Setup bonding device <bondname> on top of <bondslaves>.
     <bondslaves> is a comma-separated list of physical (ethernet) interfaces.
     <options> is a comma-separated list on bonding options (modinfo bonding for
     details) in format compatible with initscripts. If <options> includes
     multi-valued arp_ip_target option, then its values should be separated by
-    semicolon. Bond without parameters assumes
+    semicolon. if the mtu is specified, it will be set on the bond master.
+    Bond without parameters assumes
     bond=bond0:eth0,eth1:mode=balance-rr
 
 **team=**__<teammaster>__:__<teamslaves>__::