dhcp4: check if lease exists while processing arp

Also just commit when we can't init arp and close
the arp socket before we trigger a decline, which
will drop the lease (bnc#869150).
dhcp4: fixed decline message and processing (bnc#869150)
Merge pull request #197 from mtomaschewski/bnc869150

works for me also
utils: added var array copy/move helper functions
sysfs: added ipv6_ifconfig_get/set int variants
compat: added compat suse ifsysctl file utilities
Merge pull request #198 from mtomaschewski/ifsysctl

initial ifsysctl utils