kni: fix build on Ubuntu 14.04

kni: fix build on Ubuntu 14.04

Recent Ubuntu kernel 3.13.0-30.54, although based on Linux kernel 3.13.11,
already provides skb_set_hash() inline function, slightly different than
the one provided by lib/librte_eal/linuxapp/kni/ethtool/igb/kcompat.h

Ubuntu kernel 3.13.0-30.54 provides:
    * i40e/i40evf: i40e implementation for skb_set_hash
    - https://bugs.launchpad.net/bugs/1328037
    - http://changelogs.ubuntu.com/changelogs/pool/main/l/linux/linux_3.13.0-30.54/changelog

As a result, the implementation provided by kcompat.h must be skipped.
It is not appropriate to test whether LINUX_VERSION_CODE >= KERNEL_VERSION(3,13,11)
because previous Ubuntu kernel 3.13.0-29.53, already based on 3.13.11, needs to
get the implementation provided by kcompat.h

So the full Ubuntu kernel version numbering scheme must be tested:
<base kernel version>-<ABI number>.<upload number>-<flavour>
See "What does a specific Ubuntu kernel version number mean?"
and "How can we determine the version of the running kernel?"
at: https://wiki.ubuntu.com/Kernel/FAQ

Unlike RHEL_RELEASE_CODE, there is no such UBUNTU_RELEASE_CODE available out of
the box, so it needs to be crafted from the Makefile
Similarly, UBUNTU_KERNEL_CODE is generated with ABI and upload numbers.

`lsb_release -si` is first used to check whether we are running Ubuntu
`lsb_release -sr` provides release number 14.04, then converted to integer 1404
/proc/version_signature is parsed to get base kernel version, ABI and upload
numbers, and flavour is dropped

UBUNTU_KERNEL_CODE is indirectly defined using the UBUNTU_KERNEL_VERSION macro,
which in turn is defined in kcompat.h
This makes a single place to define the Ubuntu kernel version numbering scheme,
which is slightly different than the usual "shift by 8" scheme: ABI numbers can
be big (see: https://wiki.ubuntu.com/Kernel/Dev/TopicBranches), so 16-bits have
been reserved for them.

Finally, the implementaion of skb_set_hash is skipped in kcompat.h if we are
running Ubuntu 14.04 with an Ubuntu kernel >= 3.13.0-30.54

Signed-off-by: Patrice Buriez <patrice.buriez@intel.com>
[Thomas: simpler form, use tr instead of subst]
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>