Btrfs: get/set for struct header fields

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --cc fs/btrfs/Makefile
Simple merge

diff --cc fs/btrfs/TODO
Simple merge

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

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

diff --cc fs/btrfs/disk-io.c
Simple merge

diff --cc fs/btrfs/extent-tree.c
Simple merge

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

diff --cc fs/btrfs/print-tree.c
Simple merge

diff --cc fs/btrfs/quick-test.c
Simple merge

diff --cc fs/btrfs/random-test.c
Simple merge