No need to compare value two times
Pre compute hash and index for often used header names
Optimize DefaultHttpHeaders.contains(...)
Not lookup Content-Length multiple times
Revert "Pre compute hash and index for often used header names"

This reverts commit 113861186ca8a0cfb6559f8dba42347c55c44f31.
Improve DefaultHttpHeaders lookup performance
Share some code
Valide header name while calculate the index
No need to validate known header names and values