md/raid1,raid10: don't ignore IO flags

In the Linux kernel, the following vulnerability has been resolved:

md/raid1,raid10: don't ignore IO flags

If blk-wbt is enabled by default, it's found that raid write performance

is quite bad because all IO are throttled by wbt of underlying disks,

due to flag REQ_IDLE is ignored. And turns out this behaviour exist since

blk-wbt is introduced.

Other than REQ_IDLE, other flags should not be ignored as well, for

example REQ_META can be set for filesystems, clearing it can cause priority

reverse problems; And REQ_NOWAIT should not be cleared as well, because

io will wait instead of failing directly in underlying disks.

Fix those problems by keep IO flags from master bio.

Fises: f51d46d0e7cb ("md: add support for REQ_NOWAIT")