Inet6Address : Clean up and add block-guard checks.

Removes a significant of duplicated code. The main goal of this
change is to move most of the actual implementation into
Inet6AddressImpl instead of having things split between InetAddress
and Inet6AddressImpl. Note that parseNumericAddress remains in
InetAddress for now since it's called from the frameworks.

bug: 25861497

Change-Id: I263c276ae8f7d5be8fcf0d34441f0e0702e1b6b3
7 files changed