LU-10391 lnet: allow creation of IPv6 socket.

LU-10391 lnet: allow creation of IPv6 socket.

With this patch, lnet_sock_create() can make IPv6 sockets.  If an
interface and destination is given, completely different code is
needed to bind the local address.

When no interface or destination is given, an IPv6 socket is always
created, so lnet_acceptor() needs to request that IPv4 connections are
accepted as well, and lnet_sock_getaddr() needs to detect mapped v4
addresses and present them as true v4 addresses.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Iaef1c08a9afd578b60f54cc83fd2d6882a021e6b
Reviewed-on: https://review.whamcloud.com/37705
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>