Stop using LinkProperties for static configuration.

LinkProperties can represent way more complicated configurations
than what we can actually apply to interfaces. This makes it
error-prone to use it to represent static configuration, both
when trying to apply configuration coming from LinkProperties
and when trying to save configuration from current
LinkProperties.

Instead, move static configuration (IPv4 only, since we don't
support static IPv6 configuration) into a separate
StaticIpConfiguration class.

Bug: 16114392
Bug: 16893413
Change-Id: Ib33f35c004e30b6067bb20235ffa43c247d174df