Add OsConstants#ENONET to public API

DnsResolver is using ENONET to represent a sending dns query
error. The error can only happen if querying network have neither
ipv4 nor ipv6 capability. It almost certainly means the network
does not exist or no longer exists. Since Connectivity is
becoming a mainline module in S , DnsResolver is part of moudule
that is not able to use non-formal APIs. Thus, make ENONET to be
a public API to support the usage.

Bug: 178329128
Test: make update-api
Change-Id: I0d985f611ef7bd2a5935e24356139baf953e64db
3 files changed