config hook: prevent two hooks with the same settings

config hook: prevent two hooks with the same settings

A ipv4-static config with the same IPv4 address twice is senseless.
A new function zone_config_check_same_setting is introduced.
The function provides an easy way to check if a config
of the given hook has the same value for a given key.
We can now check inside hook_new if an ipv4-static or ipv6-static config
with the same value exist and break with an error.

Fixes: #11418
Signed-off-by: Jonatan Schlag <jonatan.schlag@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>