Skip IPAddr validation for "host-gateway" string
Skip IPAddr validation for "host-gateway" string

Relates to - moby/moby 40007
The above PR added support in moby, that detects if
a special string "host-gateway" is added to the IP
section of --add-host, and if true, replaces it with
a special IP value (value of --host-gateway-ip Daemon flag
which defaults to the IP of the default bridge).

This PR is needed to skip the validation for the above
feature

Signed-off-by: Arko Dasgupta <5ace5199265f07060a7b6fe8a48858e91c7682a6@docker.com>
Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

thaJeztah/cli,docker/cli,docker/cli,cpuguy83/cli,thaJeztah/cli,cpuguy83/cli