package/lxc: security bump to version 3.0.3

package/lxc: security bump to version 3.0.3

This bump also includes the fix for CVE-2018-6556 released in 3.0.2 via
commit "CVE 2018-6556: verify netns fd in lxc-user-nic": lxc-user-nic
when asked to delete a network interface will unconditionally open a
user provided path:
https://github.com/lxc/lxc/commit/c1cf54ebf251fdbad1e971679614e81649f1c032

This code path may be used by an unprivileged user to check for the
existence of a path which they wouldn't otherwise be able to reach. It
may also be used to trigger side effects by causing a (read-only) open
of special kernel files (ptmx, proc, sys).

Also add a dependency on gcc >= 4.7
(https://github.com/lxc/lxc/issues/2592)

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>