New release 2.2.51

=== Breaking changes
 - N/A

=== New features
 - Support configuring per-device IPv4 sysctl forwarding. (beae7972)
 - Support interface alternative name. (9b8be19a)
 - Introduce NetworkState and NetworkPoligy validation. (b07bd3df)

=== Bug fixes
 - kernel mode: validate conflicting routes. (ad4647e0)
 - hsr: copy mac address from port1 to port2 and hsr interfaces. (43d5ecac)
 - nm dns: interpret global-dns correctly after changes in NM. (1754abd9)
 - nm dns: differentiate empty global DNS from undefined one. (2176c951)
 - docs: Fix typo in nmstatectl man page. (4672bba4)
 - ethtool: Hide unsupported ethtool features during querying. (276cfd76)

Signed-off-by: Gris Ge <fge@redhat.com>