smb: smbdirect: introduce smbdirect_socket_init_{new,accepting}() and helpers

smb: smbdirect: introduce smbdirect_socket_init_{new,accepting}() and helpers

These will be used in order to initialize struct smbdirect_socket
with rdma.cm_id being valid from the start in order to hold
a reference to the correct net namespace, this will allow
us to implement async connecting and accepting logic in
the next steps.

This comes with some related helper functions in
order to initialize the socket without the need
to access internals of struct smbdirect_socket:

  smbdirect_socket_set_initial_parameters
  smbdirect_socket_get_current_parameters
  smbdirect_socket_set_kernel_settings
  smbdirect_socket_set_custom_workqueue

Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>