RDMA/cm: Add RDMA CM support for IBoE devices

Add support for IBoE device binding and IP --> GID resolution.  Path
resolving and multicast joining are implemented within cma.c by
filling in the responses and running callbacks in the CMA work queue.

IP --> GID resolution always yields IPv6 link local addresses; remote
GIDs are derived from the destination MAC address of the remote port.
Multicast GIDs are always mapped to multicast MACs as is done in IPv6.
(IPv4 multicast is enabled by translating IPv4 multicast addresses to
IPv6 multicast as described in
<http://www.mail-archive.com/[email protected]/msg02134.html>.)

Some helper functions are added to ib_addr.h.

Signed-off-by: Eli Cohen <[email protected]>
Signed-off-by: Roland Dreier <[email protected]>