UDP tests store a packet sequence number in the packets to detect loss
and ordering issues. This sequence number is a 32-bit signed integer,
which can wrap during very long-running UDP tests. This change adds
an option (defaulting to off) which uses a 64-bit unsigned integer to
store this quantity in the packet. The option is specified on the
client side; the server must support this feature for proper
functioning (older servers will interoperate with newer clients, as
long as --udp-counters-64-bit is not used).
The default might be changed in a future version of iperf3.
As a part of this change, the client sends its version string to the
server in the parameter block.
Uses a public-domain compatibility shim for 64-bit byte order
conversions. There are probably some additional platforms that need
to be supported, in particular Solaris. We might add some
configure-time checks to only enable this feature on platforms where
we can support the byte-order conversions.
This change is not well-tested.
Towards issue #191.
