connman: Fix NFS boot hang if connman is NETWORK_MANAGER

NFS booting hangs since connman forces the the interface to be
brought down before it will bring it up.

Signed-off-by: Muhammad Shakeel <muhammad_shakeel@mentor.com>
Merge pull request #35 from mshakeel/connman

connman: Fix NFS boot hang if connman is NETWORK_MANAGER