Improve messages about user mode a bit
No need to canonicalize fixed paths
networkd: use structured logging for links and bridges
networkd: print the received DHCPv4 address and gateway

It seems that networkd stores in_addr.s_addr contents in reverse
order (little-endian, not network order). This is a bit confusing,
but sd_rtnl evidently likes this order.
build-sys: fix distcheck