Original 2.4.x version by Angelo Dell'Aera (buffer@antifork.org)

Here is the 2.4 version with some cleanups converted to 2.6.
- use tcp_ prefix (dave)
- get rid of rwlock not needed (dave)
- do some hand optimization of the inline's
- don't make init inline
- get rid of extra whitespace
- eliminate accessor for mss_cache