LogPipe: define macro to encompass all branch related flags

To make it easier to use all branch properties assigned to a LogPipe,
define PIF_BRANCH_PROPERTIES the sum of all such flags.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
LogMultiplexer: propagate branch properties to the head of the branch

Since the compilation process doesn't always have all the context to
propagate branch-related LogPipe flags back to the head element
of the LogMultiplexer branches, do that in log_multiplexer_init().

We basically pick up "final" and "fallback" flags from Pipes on a branch
regardless if they have been set on the branch head or on subsequent
elements.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
cfg-tree: make sure final/fallback flags are applied to at least one LogPipe on a branch

In some cases (when a branch contains a source reference), the
fallback/final flags could've been missed, causing syslog-ng to ignore
them even if specified in the configuration file.

This patch together with its parent puts these flags to at least one
LogPipe instance on a branch, which is then picked by LogMultiplexer
in its init() method.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>