package/mosquitto: security bump to version 1.5.6

package/mosquitto: security bump to version 1.5.6

Fixes the following security issues:

CVE-2018-12551: If Mosquitto is configured to use a password file for
authentication, any malformed data in the password file will be treated as
valid. This typically means that the malformed data becomes a username and
no password.  If this occurs, clients can circumvent authentication and get
access to the broker by using the malformed username.  In particular, a
blank line will be treated as a valid empty username.  Other security
measures are unaffected.  Users who have only used the mosquitto_passwd
utility to create and modify their password files are unaffected by this
vulnerability.  Affects version 1.0 to 1.5.5 inclusive.

CVE-2018-12550: If an ACL file is empty, or has only blank lines or
comments, then mosquitto treats the ACL file as not being defined, which
means that no topic access is denied.  Although denying access to all topics
is not a useful configuration, this behaviour is unexpected and could lead
to access being incorrectly granted in some circumstances.  Affects versions
1.0 to 1.5.5 inclusive.

CVE-2018-12546: If a client publishes a retained message to a topic that
they have access to, and then their access to that topic is revoked, the
retained message will still be delivered to future subscribers.  This
behaviour may be undesirable in some applications, so a configuration option
check_retain_source has been introduced to enforce checking of the retained
message source on publish.

Add two upstream post-1.5.6 patches to fix a build error in the bridge code
when ADNS is enabled and when building with older toolchains not defaulting
to C99 mode.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>