kdbus: add CMD_UPDATE_METADATA ioctl (reinitialize connection metadata)

kdbus: add CMD_UPDATE_METADATA ioctl (reinitialize connection metadata)

Added to satisfy efl/launchpad developers' request.

Tizen code routinely performs the following operation sequence:
1. create kdbus connection
2. update seclabel
3. rely on updated seclabel

CONN_INFO has always returned seclabel collected at HELLO time (behavior
consistent across all kdbus versions and documented in kdbus man). This
would break step 3 of the above sequence.

KDBUS_CMD_UPDATE_METADATA ioctl updates a connection's metadata to
reflect the current state. Metadata is collected in the exact same way
as during HELLO.

Semantics Required by efl/launchpad can be obtained by altering the
sequence like so:
1. create kdbus connection
2. update seclabel
+2b. ioctl(connection_fd, KDBUS_CMD_UPDATE_METADATA);
3. rely on updated seclabel

Change-Id: I4a4b2aea4256f8bfb3bd1c0d3df5e963d243cb52
Signed-off-by: Konrad Lipinski <konrad.l@samsung.com>