Remove size restrictions from network reads

The reads now read as much of the data as is available to reduce the
number of distinct malloc calls that need to be made. The SSL_read also
now allocates the buffer before reading into it so that the amount of
copying is reduced.

Also removed some of the not quite helpful debug messages.

include/maxscale/limits.h

@@ -37,16 +37,6 @@ MXS_BEGIN_DECLS
  */
 #define MXS_SO_SNDBUF_SIZE (128 * 1024)
 
-/**
- * MXS_MAX_NW_READ_BUFFER_SIZE
- *
- * The maximum amount of data read in one gofrom a client DCB.
- *
- * TODO: Consider removing altogether so that we always read
- *       whatever is available in the socket.
- */
-#define MXS_MAX_NW_READ_BUFFER_SIZE (32 * 1024)
-
 /**
  * MXS_MAX_THREADS
  *