[netcp] Add tftp protocol options and new defaults

Add options for tftp block size and window size. Also, reduce the
default window size to 256 to relieve pressure on rx bufs.

NET-192
TO-479

Change-Id: I9023300d59f497fdc3013aff5456062d194326d3

tools: Add command line options to net*.

options:
--help Print this message.
--timeout=<msec> Set discovery timeout to <msec>.
--nowait Do not wait for first packet before timing out.

Change-Id: Ia34f337e7aeca8cab22000a92358c3fd6f0b6376

[tools] Adding netls command to discover devices

Change-Id: Ifaea41e25d57cd037f5fbcde5c3de76928c4b566