btrfs: hide typecast to definition of BTRFS_SEND_TRANS_STUB

Signed-off-by: David Sterba <dsterba@suse.cz>

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

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

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

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