coverity: remove unused pointer value

Also clarify how we use a similar pointer nearby.
coverity: remove dead code

A spurious return was added at the end of a function.
coverity: fix TOCTOU problem when creating chroot

It is believed that checking for existence of a directory or a file
before an action is useless since it could be created after the check
and before the action. Therefore, it is better to just try to do the
action and handle any failure gracefully.

When setting up the chroot, instead of checking if it already exists, we
create it and don't display an error if it is already set up.
coverity: fix a resource leak

In `netlink.c`, ensure we free the socket if we have a memory allocation
problem.
coverity: fix a memory leak

A memory leak was happening when setting the description of an interface.
coverity: remove a theoritical memory leak

If cargc is 0, cargv should not have been allocated. However, to be more
robust, let's say this is possible and handle this case correctly.
coverity: handle case where we didn't get enough place in getopt string

While not currently possible, it may become possible in the future to
forget to allocate enough place in getopt specification string to add
protocols.
coverity: don't make `-L` flag switch off version advertisement

A missing `break` was disabling version advertisement when using the
`-L` flag. Since the use of this flag is quite unlikely, don't tell
anyone...
coverity: remove dead code

Possible values for `tlv_subtype` were already checked. The default case
is not possible.
coverity: remove always false comparison

Also ensure that we use unsigned integers since we are reading unsigned
chars.
coverity: replace unsafe uses of strncpy by strlcpy
coverity: don't fallback to next case for clarity

Even if the code was correct, add an `_exit(0)` to the first branch and
do not rely on the next case for that.
coverity: if we cannot read /etc/localtime, don't go further
coverity: add code annotation to remove false positives
coverity: really fix popt issue