dhcp: log messages about invalid DHCP options
Log messages when invalid DHCP options are found. For example:
<info> dhcp4 (eth0): error parsing DHCP option 6 (domain_name_servers): address 0.0.0.0 is ignored
<info> dhcp4 (eth0): error parsing DHCP option 12 (host_name): '.example.com' is not a valid DNS domain
<info> dhcp4 (eth0): error parsing DHCP option 26 (interface_mtu): value 60 is smaller than 68