socket-util: error number to string for sockets.

For winsock2 functions, error number has to be converted to string
using FormatMessage().

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>

lib/util.c

@@ -323,6 +323,10 @@ ovs_retval_to_string(int retval)
             : ovs_strerror(retval));
 }
 
+/* This function returns the string describing the error number in 'error'
+ * for POSIX platforms.  For Windows, this function can be used for C library
+ * calls.  For socket calls that are also used in Windows, use sock_strerror()
+ * instead.  For WINAPI calls, look at ovs_lasterror_to_string(). */
 const char *
 ovs_strerror(int error)
 {