platform/linux: fix setting of IFA_ADDRESS without a peer
Since commit 9ecdba31 ('platform: create netlink messages directly without libnl-route-3') we're unconditionally setting IFA_ADDRESS to the peer address, even if there's no peer and it's all zeroes.
The kernel actually stopped caring somewhere around commit caeaba790 ('ipv6: add support of peer address') in v3.10, but Ubuntu Touch likes tu run Android's v3.4 with on some poorly supported hardware.
Fixes: 9ecdba31