linux/dim: Rename net_dim_sample() to net_dim_update_sample()

In order to avoid confusion between the function and the similarly
named struct.
In preparation for removing the 'net' prefix from dim members.

Signed-off-by: Tal Gilboa <talgi@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>