nvmet-fc: track hostport handle for associations

nvmet-fc: track hostport handle for associations

In preparation for sending LS requests for an association that
terminates, save and track the hosthandle that is part of the
LS's that are received to create associations.

Support consists of:
- Create a hostport structure that will be 1:1 mapped to a
  host port handle. The hostport structure is specific to
  a targetport.
- Whenever an association is created, create a host port for
  the hosthandle the Create Association LS was received from.
  There will be only 1 hostport structure created, with all
  associations that have the same hosthandle sharing the
  hostport structure.
- When the association is terminated, the hostport reference
  will be removed. After the last association for the host
  port is removed, the hostport will be deleted.
- Add support for the new nvmet_fc_invalidate_host() interface.
  In the past, the LLDD didn't notify loss of connectivity to
  host ports - the LLD would simply reject new requests and wait
  for the kato timeout to kill the association. Now, when host
  port connectivity is lost, the LLDD can notify the transport.
  The transport will initiate the termination of all associations
  for that host port. When the last association has been terminated
  and the hosthandle will no longer be referenced, the new
  host_release callback will be made to the lldd.
- For compatibility with prior behavior which didn't report the
  hosthandle:  the LLDD must set hosthandle to NULL. In these
  cases, not LS request will be made, and no host_release callbacks
  will be made either.

Signed-off-by: James Smart <jsmart2021@gmail.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>