mtr-packet: allow local address binding

mtr-packet: allow local address binding

A probe can be bound to a local address with the 'local-ip-4' or
'local-ip-6' arguments to 'send-probe'.  The '-a' commandline
argument to mtr will cause sent probes to be bound to the specified
address.

Changed argument names for consistency:

    'localport' is now 'local-port'
    'bitpattern' is now 'bit-pattern'

mtr now opens and connects a UDP socket at startup to determine the
local address for display in the UI.

Windows error codes resulting from send-probe are now using the
same error strings which are used to report errors in the
Unix implementation.

We now use the mtr commandline timeout value for sent probes.
Edited the help and man page to reflect that the timeout value
no longer applies to only TCP probes, but now all probes.

With this change, I believe the mtr-packet implementation is at
feature parity with mainline mtr.