conf: Options of all plugins documented

Some options are still missing descriptions though.

conf/plugins/kernel-netlink.opt

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+charon.plugins.kernel-netlink.fwmark =
+	Firewall mark to set on the routing rule that directs traffic to our routing
+	table.
+
+	Firewall mark to set on the routing rule that directs traffic to our routing
+	table. The format is [!]mark[/mask], where the optional exclamation mark
+	inverts the meaning (i.e. the rule only applies to packets that don't match
+	the mark).
+
+charon.plugins.kernel-netlink.roam_events = yes
+	Whether to trigger roam events when interfaces, addresses or routes change.
+
+charon.plugins.kernel-netlink.xfrm_acq_expires = 165
+	Lifetime of XFRM acquire state in kernel.
+
+	Lifetime of XFRM acquire state in kernel. The value gets written to
+	/proc/sys/net/core/xfrm_acq_expires. Indirectly controls the delay of XFRM
+	acquire messages sent.