Make babeld request sending conform to the RFC.

The prefix field’s size is Plen/8 rounded upwards.
Add filter to match source addresses.

Add 3 new options to configuration and manpages:
src-ip, src-eq, src-le and src-ge.
Add TLVs for source sensitive requests.
Avoid redistribution of addresses as source-specific.

Addresses should always be with source-specific, because
we want to be contact by anyone.
install-specific let disjoint prefix unchanged.

This allow to have multiple source-prefixes.
Change install-specific to a per-interface configuration.

The new option is called "source-prefix", as the
redistribute option.
Avoid sending an interface casted ss-route on that interface.
Don't cast /128 routes (probably addresses).
Update manpages: install specific as interface option.
Filter: Rename "result" to "add_metric".

The field "result" is in fact an additional cost.
Set the source prefixes through filters.

Since it's a route attribute, it fits better there.
This patch remove all references to source-prefix
in interface configuration.
Remove old source-specific configuration options.
Update manpages: source specificity set by filters.
Fix interoperability with non-ss routers.

If we change the buffered destination prefix or router ID
in a ss-update TLV, then next update TLVs will depends on
it.  This cause some interoperability problems in some
cases, and can cause wrong messages in others.

The current solution should not be definitive: we should
send all non-source-specific update in group, but the
announce-with-default-source-prefix option introduce
non-source-specific updates.