block/rnbd: Remove all likely and unlikely

block/rnbd: Remove all likely and unlikely

The IO performance test with fio after removing the likely and
unlikely macros in all if-statement shows no performance drop.
They do not help for the performance of rnbd.

The fio test did random read on 32 rnbd devices and 64 processes.
Test environment:
- AMD Opteron(tm) Processor 6386 SE
- 125G memory
- kernel version: 5.4.86
- gcc version: gcc (Debian 8.3.0-6) 8.3.0
- Infiniband controller: InfiniBand: Mellanox Technologies MT26428
[ConnectX VPI PCIe 2.0 5GT/s - IB QDR / 10GigE] (rev b0)

before
read: IOPS=549k, BW=2146MiB/s
read: IOPS=544k, BW=2125MiB/s
read: IOPS=553k, BW=2158MiB/s
read: IOPS=535k, BW=2089MiB/s
read: IOPS=543k, BW=2122MiB/s
read: IOPS=552k, BW=2154MiB/s
average: IOPS=546k, BW=2132MiB/s

after
read: IOPS=556k, BW=2172MiB/s
read: IOPS=561k, BW=2191MiB/s
read: IOPS=552k, BW=2156MiB/s
read: IOPS=551k, BW=2154MiB/s
read: IOPS=562k, BW=2194MiB/s
-----------
average: IOPS=556k, BW=2173MiB/s

The IOPS and bandwidth got better slightly after removing
likely/unlikely. (IOPS= +1.8% BW= +1.9%) But we cannot make sure
that removing the likely/unlikely help the performance because it
depends on various situations. We only make sure that removing the
likely/unlikely does not drop the performance.

Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Reviewed-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Link: https://lore.kernel.org/r/20210428061359.206794-5-gi-oh.kim@ionos.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>