udp: fix panic 'Deadlock: cycle in blocking chain'

There is a connection lock hidden in CONN_INC_REF. This lock must not
be entered when the reuselist lock is helt, the lock order is the other
way a

udp: fix panic 'Deadlock: cycle in blocking chain'

There is a connection lock hidden in CONN_INC_REF. This lock must not
be entered when the reuselist lock is helt, the lock order is the other
way around. A try enter prevents the deadlock.

refs #5392

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udp: fix crash due to race between bind and input white reuse port

In udp_do_bind foreign connections are modified (conn_reuselist is replaced)
without lock. Lock can't be obtained due to lock order

udp: fix crash due to race between bind and input white reuse port

In udp_do_bind foreign connections are modified (conn_reuselist is replaced)
without lock. Lock can't be obtained due to lock order conn_lock -> uf_lock.

As a result udp_do_bind can free a old reuselist from foreign sockets
that is currently in use by udp_input.

This is changed in a way that the reuselist is no longer replaced but
the present one is used.

Moreover, to prevent simultaneous modification of the reuselist,
udp_reuselist_add and udp_reuselist_remove are always wrapped by the
ru_lock.

refs #5215

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reuselist mutex panic: not owner

refs #4684