Fix possible buffer overflow while doing sscanf()

MAXHOSTNAMELEN + 100 is only 164 which is less than 256 sscanf() buffer.
Fix it by increasing size of nambuf buffer.
Fix potential (but not actual) buffer overflow risk.

The line buffer is 256 bytes long, so the name subfield in the line
can't be bigger than 256 bytes, but

	1) somebody could make the line buffer bigger

and

	2) this way the format item and buffer size match

so we'll do it anyway.