ss: prevent "Process" column from being printed unless requested

ss: prevent "Process" column from being printed unless requested

Commit 5883c6eba517 ("ss: show header for --processes/-p") added
"Process" to the list of columns printed by ss. However, the "Process"
header is now printed even if --processes/-p is not used.

This change aims to fix this by moving the COL_PROC column ID to the same
index as the corresponding column structure in the columns array, and
enabling it if --processes/-p is used.

Fixes: 5883c6eba517 ("ss: show header for --processes/-p")
Signed-off-by: Quentin Deslandes <qde@naccy.de>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>