Solaris 11.4 has Load Balancing for SO_REUSEPORT, but setting
SO_REUSEADDR disables load balancing. As per comments in
test/test-udp-reuseport.c prefer SO_REUSEPORT when available.
With these changes in place udp-reuseport testing passes. BIND (named),
which uses routing sockets which cause ENOPROTOOPT to be returned when
SO_REUSEPORT is requested, also continues to work with the change.
Notes:
- The use of getsockopt() to query if SO_REUSEPORT was available was
erroneous.
- Selectively limiting SO_REUSEPORT setting to specific types of socket
was considered but not entertained.
- Oracle will investigate if the setting of SO_REUSEADDR was
intentionally meant to prevent load balancing.
- Adding a test for routing sockets is left for future work.
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