ip/tunnel: Use get_addr() instead of get_prefix() for local/remote endpoints

ip/tunnel: Use get_addr() instead of get_prefix() for local/remote endpoints

Manual page ip-link(8) states that both local and remote accept
IPADDR not PREFIX. Use get_addr() instead of get_prefix() to
parse local/remote endpoint address correctly.

Force corresponding address family instead of using preferred_family
to catch weired cases as shown below.

Before this patch it is possible to create tunnel with commands:

  ip    li add dev ip6gre2 type ip6gre local fe80::1/64 remote fe80::2/64
  ip -4 li add dev ip6gre2 type ip6gre local 10.0.0.1/24 remote 10.0.0.2/24

Signed-off-by: Serhey Popovych <serhe.popovych@gmail.com>