Add ConnectivityManager.getConnectionOwnerUid()

Allow VPN apps to lookup the UID owner of a network connection.

Requires specifying the:
 - IP address and port for both the source and destination of a TCP
   connection.
 - IP address and port for either source and destination or just
   source for a UDP connection.
Only TCP and UDP protocols are supported. Only connections for UIDs
that apply to the calling VPN app will be resolved. This is intended
to replace direct app access to /proc/net/{tcp,tcp6,udp,udp6}.

The implementation uses netlink inet_diag sockets[1] to perform
the lookup on TCP sockets as well as UDP sockets when supported
(kernel has CONFIG_INET_UDP_DIAG=y).

[1] http://man7.org/linux/man-pages/man7/sock_diag.7.html

Bug: 9496886
Bug: 109758967
Test: atest HostsideVpnTests
Test: atest InetDiagSocketTest on Taimen with CONFIG_INET_UDP_DIAG
    and on Sailfish without CONFIG_INET_UDP_DIAG.
Change-Id: I2bbc7072dd091e2e653dadf6dc05024c04180f34