ifconfig(8) fails to set MTU on multiple interfaces.

[Jason Hellenthal]

>Submitter-Id:	current-users
>Originator:	Jason Hellenthal
>Organization:	
>Confidential:	no 
>Synopsis:	ifconfig(8) fails to set MTU on multiple interfaces.
>Severity:	non-critical
>Priority:	high
>Category:	kern
>Class:		sw-bug
>Release:	FreeBSD 8.3-STABLE i386
>Environment:
System: FreeBSD disbatch.DataIX.local 8.3-STABLE FreeBSD 8.3-STABLE #23 r238498: Sun Jul 15 15:34:30 EDT 2012 jh at DataIX.net:/usr/obj/usr/src/sys/DISBATCH i386

>Description:
When using ifconfig(8) to change MTU of an interface it is not allowed.

# ifconfig lagg0 mtu 1492
ifconfig: ioctl (set mtu): Invalid argument

# ifconfig dc0 mtu 1492
ifconfig: ioctl (set mtu): Invalid argument

# ifconfig dc1 mtu 1492
ifconfig: ioctl (set mtu): Invalid argument

# ifconfig pflog0 mtu 120
ifconfig: ioctl (set mtu): Invalid argument

# ifconfig ath0 mtu 1500
ifconfig: ioctl (set mtu): Invalid argument

>How-To-Repeat:

See description.

>Fix:

No workaround known.