Discard NDP packets containing null length option

[david-marchand]

Ref. NDP rfc:

[4.6]  Option Formats
...
      Length         8-bit unsigned integer.  The length of the option
                     (including the type and length fields) in units of
                     8 octets.  The value 0 is invalid.  Nodes MUST
                     silently discard an ND packet that contains an
                     option with length zero.

[david-marchand]

A first part of the fix would be to break in the loop parsing options.
Yet, there are parts of grout that continue dealing with this NDP packet where the rfc says to discard the whole packet.