Move the raw socket initialization from netd to mainline because
mainline module is going to launch clatd. Need to provide raw
socket for writing local 464xlat IPv6 packets.
Bug: 212345928
Test: flash and boot
Run "atest ClatCoordinatorTest" in a followup commit.
Change-Id: I6d1da4f1b400eeed87771ae8197b0c58ec50804b