According to NetCDF CDF 1 and 2 file format specification, the maximal
dimension size should be INT_MAX, i.e. 2^31-1, <non-negative INT>.

NetCDF file format specification:
  netcdf_file  = header data
  header       = magic numrecs dim_list gatt_list var_list
  dim_list     = ABSENT | NC_DIMENSION nelems [dim ...]
  dim          = name dim_length
  dim_length   = NON_NEG
  NON_NEG      = <non-negative INT>
  INT          = <32-bit signed integer, Bigendian, two's complement>

Note for variable size, the maximal is
  2^31-3  for CDF-1
  2^32-3  for CDF-2
  2^63-3  for CDF-5
Variable size is calculated internally in PnetCDF. Therefor, the
variable size is limited to the space available in bytes. -3 is
due to the 4-byte upward alignment.
Also, note vsize defined in the file header format is not used.