FAQ: Add entry on GRE module conflicts.

Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Justin Pettit <jpettit@nicira.com>
datapath: Check for backported sctp_compute_cksum().

This is backported by RHEL7.

Reported-by: Ashok Byahatti <ashok.byahatti@embrane.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Joe Stringer <joestringer@nicira.com>