libmemif: version 3.0

libmemif: version 3.0

Add support for multi-thread connection establishment.

- control_fd_update() callback now passes private context
  associated with updated file descriptor. File descriptor
  can belong to memif socket, memif connection or timerfd.
  In case of timerfd the context is NULL.

- memif_create_socket() new API. Creates memif socket
  handle to be passed to memif_create() in memif_conn_args_t.
  This API allows to pass private context whenever the file
  descriptor is updated.

- memif_delete_socket() new API. Deletes memif socket.
  Socket must not be in use by any interface.

Type: feature

Change-Id: I7ca4e4349595d4477195f1c32403d3e3a6eb5361
Signed-off-by: Jakub Grajciar <jgrajcia@cisco.com>