Update docs header to Magnesium in the master
Update docs header to Magnesium in the master

Should be Magnesium on master and Sodium on stable/sodium.

Signed-off-by: Anushka Bhandari <4dd523e5affe928977d73a071241bbe05895f3d3@iiitd.ac.in>
Change-Id: I97861f561d1c156cd5c28b31adc87b716f1d3a25

opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt