Before this patch, the 'KnownMasterList' field of the 'NotPrimaryMaster'
was expected to be structured in the following way:

	ArrayHeader (KnownMasterList)

	    ArrayHeader (KnownMaster)

		ArrayHeader (Address)

		    Host (string)
		    Port (uint16)

However NEO/py sends the following structure:

	ArrayHeader (KnownMasterList)

	    ArrayHeader (Address)

		Host (string)
		Port (uint16)

This also makes sense, as 'KnownMaster' doesn't need to add another
nesting, because it only includes the address.

This patch amends the NEO/go protocol definition to transparently
represent the nesting as it's send by NEO/py. See also
levin.zimmermann/neoppod@18287612 for a similar issue.

/reviewed-by @kirr
/reviewed-on !6