util: minify some code

Signed-off-by: Steven Barth <steven@midlink.org>
util: use netlink to add / remove routes

Signed-off-by: Steven Barth <steven@midlink.org>
util: redefine get_local_address using socket API

Signed-off-by: Steven Barth <steven@midlink.org>
send_hello: fix mixed code and definition

Signed-off-by: Steven Barth <steven@midlink.org>
Add missing sys/time.h include to fix musl

Signed-off-by: Steven Barth <steven@midlink.org>