USN-4969-3: DHCP regression

USN-4969-3: DHCP regression

USN-4969-1 fixed a vulnerability in DHCP. The package for Ubuntu 21.04
introduced a regression causing it to reject certain valid configuration
files. This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

Jon Franklin and Pawel Wieczorkiewicz discovered that DHCP incorrectly
handled lease file parsing. A remote attacker could possibly use this issue
to cause DHCP to crash, resulting in a denial of service.
Source: USN-4969-3: DHCP regression