packages: set more explicit ABI_VERSION values

packages: set more explicit ABI_VERSION values

In the case of upstream libraries, set the ABI_VERSION variable to the
soname value of the first version version after the last backwards
incompatible change.

For custom OpenWrt libraries, set the ABI_VERSION to the date of the
last Git commit doing backwards incompatible changes to the source,
such as changing function singatures or dropping exported symbols.

The soname values have been determined by either checking
https://abi-laboratory.pro/index.php?view=tracker or - in the case
of OpenWrt libraries - by carefully reviewing the changes made to
header files thorough the corresponding Git history.

In the future, the ABI_VERSION values must be bumped whenever the
library is updated to an incpompatible version but not with every
package update, in order to reduce the dependency churn in the
binary package repository.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>