Socket I/F: Add recvfrom() method to interface.

net/socket/socket.h

@@ -431,13 +431,46 @@ int net_timeo(systime_t start_time, socktimeo_t timeo);
  *     In this case the process will also receive a SIGPIPE unless
  *     MSG_NOSIGNAL is set.
  *
- * Assumptions:
- *
  ****************************************************************************/
 
 ssize_t psock_send(FAR struct socket *psock, FAR const void *buf, size_t len,
                    int flags);
 
+/****************************************************************************
+ * Name: inet_recvfrom
+ *
+ * Description:
+ *   Implements the socket recvfrom interface for the case of the AF_INET
+ *   and AF_INET6 address families.  inet_recvfrom() receives messages from
+ *   a socket, and may be used to receive data on a socket whether or not it
+ *   is connection-oriented.
+ *
+ *   If 'from' is not NULL, and the underlying protocol provides the source
+ *   address, this source address is filled in.  The argument 'fromlen' is
+ *   initialized to the size of the buffer associated with from, and
+ *   modified on return to indicate the actual size of the address stored
+ *   there.
+ *
+ * Parameters:
+ *   psock    A pointer to a NuttX-specific, internal socket structure
+ *   buf      Buffer to receive data
+ *   len      Length of buffer
+ *   flags    Receive flags
+ *   from     Address of source (may be NULL)
+ *   fromlen  The length of the address structure
+ *
+ * Returned Value:
+ *   On success, returns the number of characters received.  If no data is
+ *   available to be received and the peer has performed an orderly shutdown,
+ *   recv() will return 0.  Otherwise, on errors, a negated errno value is
+ *   returned (see recvfrom() for the list of appropriate error values).
+ *
+ ****************************************************************************/
+
+ssize_t inet_recvfrom(FAR struct socket *psock, FAR void *buf, size_t len,
+                      int flags, FAR struct sockaddr *from,
+                      FAR socklen_t *fromlen);
+
 #undef EXTERN
 #if defined(__cplusplus)
 }