netdev-linux: Fix build with old kernel headers.

netdev-linux: Fix build with old kernel headers.

Commit 677d9158fc0a (netdev-linux: Support for SFQ, FQ_CoDel and CoDel
qdiscs.) added support for new qdiscs.  The commit uses TCA_CODEL_* and
TCA_FQ_CODEL_* not in old kernel headers, causing a build failure against
such headers.  This commit should fix the problem by defining these values
ourselves.  (I haven't tested it against old headers, so I might have
missed something, but it's a straightforward change and at worst won't do
harm.)

It appears that sfq (also added by the same commit) was in Linux before
2.6.32, so it seems unlikely that we need any compatibility code there.

CC: Jonathan Vestin <jonavest@kau.se>
Signed-off-by: Ben Pfaff <blp@nicira.com>