Introduce ena_increase_stat() function to increase statistics by a
certain number.
The function includes the
    - lock aquire (on 32bit machines)
    - stat increase
    - lock release (on 32bit machines)

line sequence that is ubiquitous across the driver.

The function increases a single stat at a time and several stats which
are increased together weren't put into a function to avoid
calling the function several times for each stat which looks bad and
might decrease performance.
Signed-off-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>