WIP: patches/openwrt: Add link signature to packages

This should in future replace potentially automatic package version bumping patch. This should be cleaner solution for same problem as it won't tamper with versions and does not need server-side database.

Problem with tampering with version is that matching version exactly was then pretty much broken. Once package was bumped the version did not match. It is impossible to update dependency easily enough when package bump occurs.

The idea is that updater just matches signature that should be consistent between builds (unless dynamic link dependencies changed of course). When build results to package with different link dependencies then signature changes and updater reinstall such package to version from repository that is consistent. Version stays the same all the time.

Signature is generated from two sources. Dynamic library names and dynamic symbols that are linked to those libraries are included.

This is not yet fully ready. There has to be a change in updater and also I want to see how often this signature changes before we release this to the wild.

Anyway once this is used with updater changes and by removing original package version bumping patch it should fix https://gitlab.labs.nic.cz/turris/turris-build/issues/154 and https://gitlab.labs.nic.cz/turris/turris-os-packages/issues/417 and making following issue obsolete https://gitlab.labs.nic.cz/turris/turris-build/issues/41.