7176485: (bf) Allow temporary buffer cache to grow to IOV_MAX

[Alan Bateman]

This one relates to the temporary buffer cache, used to cache direct 
direct buffers for applications that do I/O with buffers that are backed 
by byte arrays in the heap. Currently the temporary buffer cache can 
cache up to 8 buffer and this should be sufficient for most scattering 
read and gathering write operations. There are however extreme cases 
where the number of buffers in the array is higher and those cases take 
a big malloc/free hit once they go beyond 8 buffers. The patch proposed 
here changes the limit so that it matches IOV_MAX. Note that there isn't 
a regression test with this because this area is covered by existing 
tests and the changes are just to help the performance for this scenario.

http://cr.openjdk.java.net/~alanb/7176485/webrev/

-Alan.