Inconsistent parameters regarding internal resource allocation

Both configurations of the LWIP library use inconsistent values in internal resource management:

• The Library allow application to allocate more application buffers (pbuf) than it can handle TCP-segment buffers (segbuf). This results in situation that allocation of pbuf succeeds but trying to send data fails with "out of memory" because no free segbuf exists. It is expected, than after allocating a pbuf has succeeded, the send operation succeeds as well
• Although the number of the in frame messages has been increased in the "netField" variant of the library, this has no effect since the number of zero copy pbuf's is still the same.

The parameters used in internal resource management needs to be fixed to match each other. The fix is required for all versions of the library.