Add method to query free send buffer size


ndb/include/transporter/TransporterRegistry.hpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/SCI_Transporter.cpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/SCI_Transporter.hpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/SHM_Buffer.hpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/SHM_Transporter.cpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/SHM_Transporter.hpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/SendBuffer.cpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/SendBuffer.hpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/TCP_Transporter.cpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/TCP_Transporter.hpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/Transporter.hpp:
  Allow accessing free send buffer size
ndb/src/common/transporter/TransporterRegistry.cpp:
  Allow accessing free send buffer size
ndb/src/mgmsrv/ConfigInfo.cpp:
  Increse min values for SHM and TCP transport send buffer size