ip-neighbor: fix ip6_ra_cmd

The option parsing loop had "break" statements included in each
'if (unformat (line_input, "this-option ...") option_values=xxx;'
statement.

Result: the code would silently ignore all but the first
option. Probably broken forever, not easy to spot because the code
looks OK even though it's badly broken.

Type: fix

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: I667bee85b4ca654b53fb3af421f957957ed0f0f8