net/smc: Support SO_REUSEPORT

This enables SO_REUSEPORT [1] for clcsock when it is set on smc socket,
so that some applications which uses it can be transparently replaced
with SMC. Also, this helps improve load distribution.

Here is a simple test of NGINX + wrk with SMC. The CPU usage is collected
on NGINX (server) side as below.

Disable SO_REUSEPORT:

05:15:33 PM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
05:15:34 PM all 7.02 0.00 11.86 0.00 2.04 8.93 0.00 0.00 0.00 70.15
05:15:34 PM 0 0.00 0.00 0.00 0.00 16.00 70.00 0.00 0.00 0.00 14.00
05:15:34 PM 1 11.58 0.00 22.11 0.00 0.00 0.00 0.00 0.00 0.00 66.32
05:15:34 PM 2 1.00 0.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 98.00
05:15:34 PM 3 16.84 0.00 30.53 0.00 0.00 0.00 0.00 0.00 0.00 52.63
05:15:34 PM 4 28.72 0.00 44.68 0.00 0.00 0.00 0.00 0.00 0.00 26.60
05:15:34 PM 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
05:15:34 PM 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
05:15:34 PM 7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00

Enable SO_REUSEPORT:

05:15:20 PM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
05:15:21 PM all 8.56 0.00 14.40 0.00 2.20 9.86 0.00 0.00 0.00 64.98
05:15:21 PM 0 0.00 0.00 4.08 0.00 14.29 76.53 0.00 0.00 0.00 5.10
05:15:21 PM 1 9.09 0.00 16.16 0.00 1.01 0.00 0.00 0.00 0.00 73.74
05:15:21 PM 2 9.38 0.00 16.67 0.00 1.04 0.00 0.00 0.00 0.00 72.92
05:15:21 PM 3 10.42 0.00 17.71 0.00 1.04 0.00 0.00 0.00 0.00 70.83
05:15:21 PM 4 9.57 0.00 15.96 0.00 0.00 0.00 0.00 0.00 0.00 74.47
05:15:21 PM 5 9.18 0.00 15.31 0.00 0.00 1.02 0.00 0.00 0.00 74.49
05:15:21 PM 6 8.60 0.00 15.05 0.00 0.00 0.00 0.00 0.00 0.00 76.34
05:15:21 PM 7 12.37 0.00 14.43 0.00 0.00 0.00 0.00 0.00 0.00 73.20

Using SO_REUSEPORT helps the load distribution of NGINX be more
balanced.

[1] https://man7.org/linux/man-pages/man7/socket.7.html

Signed-off-by: Tony Lu <tonylu@linux.alibaba.com>
Acked-by: Wenjia Zhang <wenjia@linux.ibm.com>
Link: https://lore.kernel.org/r/20220922121906.72406-1-tonylu@linux.alibaba.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>