net/mlx5e: Rename physical symbol errors counter

Rename rx_symbol_errors_phy to rx_pcs_symbol_err_phy, in order to
prevent confusion with rx_symbol_err_phy counter.

rx_pcs_symbol_err_phy counter counts the number of symbol errors that
were detected on the PCS (regardless of traffic) and weren't
corrected by FEC correction algorithm or that FEC algorithm was
not active on this interface.

rx_symbol_err_phy refers to errors on packet level (physical error
during a packet receive).

Fixes: 5db0a4f6 ("net/mlx5e: Expose physical layer statistical...")
Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Cc: kernel-team@fb.com