Displaying the supported module types of a network adapter

[Alan Somers]

SIOCGIFMEDIA will return the list of supported media types and the
current media type of a network interface.  But for NICs with
pluggable modules (SFP+, QSFP, etc), it would also be useful to know
the allowed module type.  I can't find any way to determine that using
the standard tools.  cxgbe(4) is aware of the module type allowed by
the card, but doesn't expose that information to userspace.  I can add
a simple sysctl to do so, but it would be better to add a standard
ioctl that can be used by all network drivers.

Besides cxgbe(4), can any other network drivers support this?  If so,
would anybody else be interested?  If so, should I add it to the
"ifconfig -v" output?

-Alan