The check for a TLV going beyond the end of the packet was off by two.
A malformed packet could possibly cause babeld to read two octets beyond
the end of the read buffer.

While technically a buffer overflow, this is most probably not
exploitable, since it is a read-only overflow.  At worst, it would
cause two octets of garbage to be parsed and treated as valid data.

This fixes a bug that was introduced in commit 4f4e3cba, and prevented
non-source-specific IPv4 routes from being redistributed.  Thanks
to Niklas Yann Wettengel for the detective work.

Point-to-point interfaces are bound to two link-local addresses: the
local address and the peer address [1].  The former is advertised with
an IFA_LOCAL TLV and the latter with an IFA_ADDRESS TLV.

[1] $ip addr show [...]
    inet6 fe80::1234 peer fe80::5678/128 scope link

Since send_request was buggy, these weren't doing anything.  Don't change
the behaviour, sending wildcard requests at startup is not a good idea.

When we lose a route and have no feasible alternate, we should send requests
straight away rather than waiting for a periodic update.  If we have an
unfeasible route, send according to that route and resend, otherwise do
a multicast.

Reported by janus.

This also removes special casing of late Hellos.

- Hello is not ignored if there is a mandatory sub-TLV,
- non-wildcard Updates also,
- Duplicated check for Requests,
- wrong size for the beginning of sub-TLVs for Seqno Requests,
- wrong size for source specific Requests and Seqno Requests.

That patch was fixing a little bug, but makes another bigger one.
The previous patch fixes both.

This reverts commit e687a58f.

Quiet git more.

Share the data better.

route.c was the only routine in all of babeld that had tabs creep in.