sixlowpan/ipv6: Simplify sending of ICMPv6 packets for sixlowpan neighbor discovery

[miri64]

By now, the functions for sending ICMPv6 packets (icmpv6_send_* in sixlowpan/icmp.h) using one 8-bit number as parameter for every possible option they can carry and the options are then set very rigid (and in some cases redundant) by those functions. A more configurable and less parameter demanding solution might be more sufficient.

[OlegHahm]

I like the "more sufficient" part. scnr

[mehlis]

follow up for #644

[kaspar030]

(sixlowpan: ...)

[mehlis]

@authmillenon is this idea still valid?

[miri64]

Yes.