Add tests for pw -N

PR:		150449
Submitted by:	Robert O'Neil <oneil.rs@gmail.com>
Approved by:	will


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275829 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
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


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275830 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f