RDMA/core: Add support for iWARP Port Mapper user space service

RDMA/core: Add support for iWARP Port Mapper user space service

This patch adds iWARP Port Mapper (IWPM) Version 2 support.  The iWARP
Port Mapper implementation is based on the port mapper specification
section in the Sockets Direct Protocol paper -
http://www.rdmaconsortium.org/home/draft-pinkerton-iwarp-sdp-v1.0.pdf

Existing iWARP RDMA providers use the same IP address as the native
TCP/IP stack when creating RDMA connections.  They need a mechanism to
claim the TCP ports used for RDMA connections to prevent TCP port
collisions when other host applications use TCP ports.  The iWARP Port
Mapper provides a standard mechanism to accomplish this.  Without this
service it is possible for RDMA application to bind/listen on the same
port which is already being used by native TCP host application.  If
that happens the incoming TCP connection data can be passed to the
RDMA stack with error.

The iWARP Port Mapper solution doesn't contain any changes to the
existing network stack in the kernel space.  All the changes are
contained with the infiniband tree and also in user space.

The iWARP Port Mapper service is implemented as a user space daemon
process.  Source for the IWPM service is located at
http://git.openfabrics.org/git?p=~tnikolova/libiwpm-1.0.0/.git;a=summary

The iWARP driver (port mapper client) sends to the IWPM service the
local IP address and TCP port it has received from the RDMA
application, when starting a connection.  The IWPM service performs a
socket bind from user space to get an available TCP port, called a
mapped port, and communicates it back to the client.  In that sense,
the IWPM service is used to map the TCP port, which the RDMA
application uses to any port available from the host TCP port
space. The mapped ports are used in iWARP RDMA connections to avoid
collisions with native TCP stack which is aware that these ports are
taken. When an RDMA connection using a mapped port is terminated, the
client notifies the IWPM service, which then releases the TCP port.

The message exchange between the IWPM service and the iWARP drivers
(between user space and kernel space) is implemented using netlink
sockets.

1) Netlink interface functions are added: ibnl_unicast() and
   ibnl_mulitcast() for sending netlink messages to user space

2) The signature of the existing ibnl_put_msg() is changed to be more
   generic

3) Two netlink clients are added: RDMA_NL_NES, RDMA_NL_C4IW
   corresponding to the two iWarp drivers - nes and cxgb4 which use
   the IWPM service

4) Enums are added to enumerate the attributes in the netlink
   messages, which are exchanged between the user space IWPM service
   and the iWARP drivers

Signed-off-by: Tatyana Nikolova <tatyana.e.nikolova@intel.com>
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: PJ Waskiewicz <pj.waskiewicz@solidfire.com>
[ Fold in range checking fixes and nlh_next removal as suggested by Dan
  Carpenter and Steve Wise.  Fix sparse endianness in hash.  - Roland ]

Signed-off-by: Roland Dreier <roland@purestorage.com>