IB/ipoib: Set device connection mode only when needed

IB/ipoib: Set device connection mode only when needed

When changing the connection mode, the ipoib_set_mode function
did not check if the previous connection mode equals to the
new one. This commit adds the required check and return 0 if the new
mode equals to the previous one.

Fixes: 839fcaba355a ("IPoIB: Connected mode experimental support")
Signed-off-by: Feras Daoud <[email protected]>
Signed-off-by: Erez Shitrit <[email protected]>
Reviewed-by: Alex Vesker <[email protected]>
Reviewed-by: Yuval Shaia <[email protected]>
Signed-off-by: Leon Romanovsky <[email protected]>
Signed-off-by: Doug Ledford <[email protected]>