Add support for IP over infiniband, IPoIB, to lagg(4). Currently only
the failover protocol is supported due to limitations in the IPoIB
architecture. Refer to the lagg(4) manual page for how to configure
and use this new feature. A new network interface type,
IFT_INFINIBANDLAG, has been added, similar to the existing
IFT_IEEE8023ADLAG .

ifconfig(8) has been updated to accept a new laggtype argument when
creating lagg(4) network interfaces. This new argument is used to
distinguish between ethernet and infiniband type of lagg(4) network
interface. The laggtype argument is optional and defaults to
ethernet. The lagg(4) command line syntax is backwards compatible.

Differential Revision: https://reviews.freebsd.org/D26254
Reviewed by: melifaro@
MFC after: 1 week
Sponsored by: Mellanox Technologies // NVIDIA Networking