Use the POSIX limits.h define of PATH_MAX for maximum path length.

This has been being hit in pushbuild


ndb/include/util/File.hpp:
  use PATH_MAX for maximum filename length
ndb/src/common/portlib/NdbConfig.c:
  use PATH_MAX for max path name length instead of hardcoding 128
ndb/src/common/util/File.cpp:
  use PATH_MAX for maximum filename length