Fix IP version field and hop limit in keyed IPv6 tunnel app

The IP version field was set incorrectly.

The default hop limit was changed from 0 to 64 and made configurable.
Update authorized_keys
Added signatures of sleep(3), alarm(3) and ualarm(3) to
src/core/clib.sh .
Added module lib.watchdog.watchdog .
Adjusted src/Makefile to run **/selftest.sh scripts.
[lib.watchdog.watchdog] Fixed a comment.
Merge pull request #232 from eugeneia/watchdog

Added watchdog module.
Merge pull request #226 from korczis/patch-1

Update authorized_keys
Merge pull request #223 from alexandergall/keyed-ipv6-tunnel-fix

Fix IP version field and hop limit in keyed IPv6 tunnel app