clat: split read_packet in twain

This does introduce some duplication, but this is
to facilitate later changes to how AF_PACKET read works.
Switching from read() to recvmsg(), processing cmsg's, etc...

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I8368d58d2cec88bafa688c38d63347fa898f3ad7
1 file changed