Close#2040
* commit '06af130bb7c042d8a44720cc9423b3fc76deadee':
- DHCP: fix crash after adding static lease which replaces the dynamic one
* DHCP: don't replace the host name from static lease
When a static lease contains a host name
and client sends its own host name:
1. don't replace the host name from static lease with it
2. send option FQDN to the client in Ack response packet