flow_dissect: call init_default_flow_dissectors() earlier

BugLink: https://bugs.launchpad.net/bugs/1645278

Andre Noll reported panics after my recent fix (commit 34fad54c
"net: __skb_flow_dissect() must cap its return value")

After some more headaches, Alexander root caused the problem to
init_default_flow_dissectors() being called too late, in case
a network driver like IGB is not a module and receives DHCP message
very early.

Fix is to call init_default_flow_dissectors() much earlier,
as it is a core infrastructure and does not depend on another
kernel service.

Fixes: 06635a35 ("flow_dissect: use programable dissector in skb_flow_dissect and friends")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andre Noll <maan@tuebingen.mpg.de>
Diagnosed-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit c9b8af13)
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>

net/core/flow_dissector.c

@@ -949,4 +949,4 @@ static int __init init_default_flow_dissectors(void)
 	return 0;
 }
 
-late_initcall_sync(init_default_flow_dissectors);
+core_initcall(init_default_flow_dissectors);