soreuseport: BPF selection functional test for TCP

Unfortunately the existing test relied on packet payload in order to
map incoming packets to sockets.  In order to get this to work with TCP,
TCP_FASTOPEN needed to be used.

Since the fast open path is slightly different than the standard TCP path,
I created a second test which sends to reuseport group members based
on receiving cpu core id.  This will probably serve as a better
real-world example use as well.

Signed-off-by: Craig Gallek <kraig@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>