RDMA/core/iwpm_msg: Add proper descriptions for 'skb' param

Fixes the following W=1 kernel build warning(s):

drivers/infiniband/core/iwpm_msg.c:402: warning: Function parameter or member 'skb' not described in 'iwpm_register_pid_cb'
drivers/infiniband/core/iwpm_msg.c:475: warning: Function parameter or member 'skb' not described in 'iwpm_add_mapping_cb'
drivers/infiniband/core/iwpm_msg.c:553: warning: Function parameter or member 'skb' not described in 'iwpm_add_and_query_mapping_cb'
drivers/infiniband/core/iwpm_msg.c:636: warning: Function parameter or member 'skb' not described in 'iwpm_remote_info_cb'
drivers/infiniband/core/iwpm_msg.c:716: warning: Function parameter or member 'skb' not described in 'iwpm_mapping_info_cb'
drivers/infiniband/core/iwpm_msg.c:773: warning: Function parameter or member 'skb' not described in 'iwpm_ack_mapping_info_cb'
drivers/infiniband/core/iwpm_msg.c:803: warning: Function parameter or member 'skb' not described in 'iwpm_mapping_error_cb'
drivers/infiniband/core/iwpm_msg.c:851: warning: Function parameter or member 'skb' not described in 'iwpm_hello_cb'

Link: https://lore.kernel.org/r/[e-mail]
Cc: Doug Ledford <[e-mail]>
Cc: Jason Gunthorpe <[e-mail]>
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

drivers/infiniband/core/iwpm_msg.c

···
 /**
  * iwpm_register_pid_cb - Process the port mapper response to
  *                        iwpm_register_pid query
- * @skb:
+ * @skb: The socket buffer
  * @cb: Contains the received message (payload and netlink header)
  *
  * If successful, the function receives the userspace port mapper pid
···
 /**
  * iwpm_add_mapping_cb - Process the port mapper response to
  *                       iwpm_add_mapping request
- * @skb:
+ * @skb: The socket buffer
  * @cb: Contains the received message (payload and netlink header)
  */
 int iwpm_add_mapping_cb(struct sk_buff *skb, struct netlink_callback *cb)
···
 /**
  * iwpm_add_and_query_mapping_cb - Process the port mapper response to
  *                                 iwpm_add_and_query_mapping request
- * @skb:
+ * @skb: The socket buffer
  * @cb: Contains the received message (payload and netlink header)
  */
 int iwpm_add_and_query_mapping_cb(struct sk_buff *skb,
···
 /**
  * iwpm_remote_info_cb - Process remote connecting peer address info, which
  *                       the port mapper has received from the connecting peer
- * @skb:
+ * @skb: The socket buffer
  * @cb: Contains the received message (payload and netlink header)
  *
  * Stores the IPv4/IPv6 address info in a hash table
···
 /**
  * iwpm_mapping_info_cb - Process a notification that the userspace
  *                        port mapper daemon is started
- * @skb:
+ * @skb: The socket buffer
  * @cb: Contains the received message (payload and netlink header)
  *
  * Using the received port mapper pid, send all the local mapping
···
 /**
  * iwpm_ack_mapping_info_cb - Process the port mapper ack for
  *                            the provided local mapping info records
- * @skb:
+ * @skb: The socket buffer
  * @cb: Contains the received message (payload and netlink header)
  */
 int iwpm_ack_mapping_info_cb(struct sk_buff *skb, struct netlink_callback *cb)
···
 /**
  * iwpm_mapping_error_cb - Process port mapper notification for error
  *
- * @skb:
+ * @skb: The socket buffer
  * @cb: Contains the received message (payload and netlink header)
  */
 int iwpm_mapping_error_cb(struct sk_buff *skb, struct netlink_callback *cb)
···
 /**
  * iwpm_hello_cb - Process a hello message from iwpmd
  *
- * @skb:
+ * @skb: The socket buffer
  * @cb: Contains the received message (payload and netlink header)
  *
  * Using the received port mapper pid, send the kernel's abi_version