btrfs: annotate as unlikely fs aborted checks in space flushing code

btrfs: annotate as unlikely fs aborted checks in space flushing code

It's not expected to have the fs in an aborted state, so surround the
abortion checks with unlikely to make it clear it's unexpected and to
hint the compiler to generate better code.

Also at maybe_fail_all_tickets() untangle all repeated checks for the
abortion into a single if-then-else. This makes things more readable
and makes the compiler generate less code. On x86_64 with gcc 14.2.0-19
from Debian I got the following object size differences.

Before this change:

  $ size fs/btrfs/btrfs.ko
     text	   data	    bss	    dec	    hex	filename
  2021606	 179704	  25088	2226398	 21f8de	fs/btrfs/btrfs.ko

After this change:

  $ size fs/btrfs/btrfs.ko
     text	   data	    bss	    dec	    hex	filename
  2021458	 179704	  25088	2226250	 21f84a	fs/btrfs/btrfs.ko

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>