build: fix soname info for 19.11 compatibility

build: fix soname info for 19.11 compatibility

The soname for each stable ABI version should be just the ABI version major
number without the minor number. Unfortunately both major and minor were
used causing version 20.1 to be incompatible with 20.0.

This patch fixes the issue by switching from 2-part to 3-part ABI version
numbers so that we can keep 20.0 as soname and using the final digits to
identify the 20.x releases which are ABI compatible. This requires changes
to both make and meson builds to handle the three-digit version and shrink
it to 2-digit for soname.

The final fix needed in this patch is to adjust the library version number
for the ethtool example library, which needs to be upped to 2-digits, as
external libraries using the DPDK build system also use the logic in this
file.

Fixes: cba806e07d6f ("build: change ABI versioning to global")

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Tested-by: Ray Kinsella <mdr@ashroe.eu>
Tested-by: Ferruh Yigit <ferruh.yigit@intel.com>
Tested-by: Kevin Laatz <kevin.laatz@intel.com>
Tested-by: David Marchand <david.marchand@redhat.com>