Add tests for pw -N

PR:		150449
Submitted by:	Robert O'Neil <oneil.rs@gmail.com>
Approved by:	will
Add ability to not specify a zone identifier twice, when both source and
destination addresses are specified.
For example:
	# ping6 -S fe80::1%ix0 ff02::1
or
	# ping6 -S fe80::1 fe80::2%ix0

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC