fastd: enable connecting using IPv6

attention: this includes a MTU change which also has to be adopted on the node side
fastd: make mtu configurable

fastd over ipv6 needs a smaller mtu due to the bigger ipv6 header
compared to ipv4. we do not set this new mtu directly, as communities
need to change the mtu on all nodes in the network
Merge branch 'master' into mtu-fastd

Conflicts:
	manifests/init.pp
	templates/etc/fastd/fastd.conf.erb
Update readme with fastd mtu
Merge pull request #48 from ohrensessel/mtu-fastd

make fastd mtu configurable