ndb: increase buffer size to allow longer lines

when reading a long line such as a dkim key in a
txt record, ndb calls Brdstr, which is limited
to the size of the buffer. This means we would
fail to parse the line from NDB, and bail out
early.

Increasing the buffer size allows us to read and
parse longer lines.

sys/include/ndb.h

@@ -27,7 +27,7 @@ struct Ndb
 	Ndb		*next;
 
 	Biobufhdr	b;		/* buffered input file */
-	uchar		buf[256];	/* and its buffer */
+	uchar		buf[8192];	/* and its buffer */
 
 	ulong		mtime;		/* mtime of db file */
 	Qid		qid;		/* qid of db file */