network: accept all values provided by kernel

network: accept all values provided by kernel

Follow-up for af493fb742bece2cafcdbab9238c711ac9090c9f.

The kernel sends FRA_SUPPRESS_IFGROUP attribute with -1, that must be
handled by networkd.

For FRA_SUPPRESS_PREFIXLEN, we already handled -1, but ignored values
larger than 128. We should not configure rules with such a meaningless
value, but should manage such rules when received from kernel. It can
occur when created by other tools mistakenly. If networkd ignores them,
then networkd cannot remove them.