Btrfs: add a type field for the transaction handle

This patch add a type field into the transaction handle structure,
in this way, we needn't implement various end-transaction functions
and can make the code more simple and readable.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>

diff --cc fs/btrfs/inode.c
Simple merge

diff --cc fs/btrfs/transaction.c
Simple merge

diff --cc fs/btrfs/transaction.h
Simple merge