client: added ipv4 arp verify and notify utilities
arp: use more likely to work gratuitous ARP requests
address: allow to mark address tentative/duplicate
addrconf: mark static lease addresses tentative
ipv6: corrected to apply inverted ipv6.enable flag
arp: verify ipv4 addresses by default (fate#314399)

Enabled arp verify for ipv4 addresses by default (RFC 5227)
and send arp notify when requested in suse ifcfg variables
CHECK_DUPLICATE_IP(=yes) and SEND_GRATUITOUS_ARP(=no).
compat: fixed to disable ip for BOOTPROTO none
Merge pull request #190 from mtomaschewski/ipv4-dad

verify [static] ipv4 addresses by default (fate#314399)
address: return NULL instead to fail in assert
netlink: trace address parsing as event in debug3
netlink: fixed tunnel ipv6 link address parsing
netlink: parse link hwpeer alias hwbrd address

The content depends on the IFF_POINTOPOINT flag; when set
is has to be interpreted as peer otherwise as brd. We use
a single hwpeer variable in the link struct for both.
Merge pull request #191 from mtomaschewski/address-parsing

netlink address parsing fixes