Add support for SO_REUSEPORT

A DESCRIPTION OF THE REQUEST :
There is no way to access the SO_REUSEPORT socket option in the JDK. The addition of a setReusePort() and getReusePort() function equivalent to setReuseAddress() and getReuseAddress() would fill this gap.

Alternatively, a more generic way of setting and querying individual socket options would suffice.

JUSTIFICATION :
Quite a lot of peer to peer systems are now making use of this flag in order to avoid having to configure many ports on network address translators. With this flag, both outgoing and incoming connections can be bound to the same port and consequently remain bound to the same external port of the NAT.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Add setReusePort() and getReusePort() to the JDK.
ACTUAL -
Not applicable.

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CUSTOMER SUBMITTED WORKAROUND :
Not applicable.