[CLATJ#12] ClatCoordinator: open packet socket with a given mark

Move the packet socket initialization from netd to jni because
mainline module is going to launch clatd. Need to provide packet
socket for reading local 464xlat IPv6 packets.

Bug: 212345928
Test: flash and boot
Run "atest ClatCoordinatorTest" in a followup commit.

Change-Id: I1cef6e099403f883d668081fb5e917863f5a3c2a
2 files changed