networkd: improve DHCP error logging
sd-dhcp-client: don't fail hard if UDP socket can not be bound

Even if we cannot renew the lease at T1, we will likely succeed at T2, so warn and ignore the failure.

This could happen if for whatever reason the received address is not yet configured, or it has
been lost.
networkd: dhcp - update the lifetime of an existing address

The logic otherwise is that we leave anything preconfigured alone, but in the case of DHCP
we actually need to update it whenever the lease is renewed.