net/rds: An rds_sock is added too early to the hash table

In rds_bind(), an rds_sock is added to the RDS bind hash table before
rs_transport is set.  This means that the socket can be found by the
receive code path when rs_transport is NULL.  And the receive code
path de-references rs_transport for congestion update check.  This can
cause a panic.  An rds_sock should not be added to the bind hash table
before all the needed fields are set.

Reported-by:  <syzbot+4b4f8163c2e246df3c4c@syzkaller.appspotmail.com>
Signed-off-by: Ka-Cheong Poon <ka-cheong.poon@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>