utils: Do not reset family for default, any, all addresses

utils: Do not reset family for default, any, all addresses

Thomas reported a change in behavior with respect to autodectecting
address families. Specifically, 'ip ro add default via fe80::1'
syntax was failing to treat fe80::1 as an IPv6 address as it did in
prior releases. The root causes appears to be a change in family when
the default keyword is parsed.

'default', 'any' and 'all' are relevant outside of AF_INET. Leave the
family arg as is for these when setting addr.

Fixes: 93fa12418dc6 ("utils: Always specify family and ->bytelen in get_prefix_1()")
Reported-by: Thomas Deutschmann <whissi@gentoo.org>
Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Serhey Popovych <serhe.popovych@gmail.com>