CLEANUP: atomic/tree-wide: replace single increments/decrements with inc/dec

This patch replaces roughly all occurrences of an HA_ATOMIC_ADD(&foo, 1)
or HA_ATOMIC_SUB(&foo, 1) with the equivalent HA_ATOMIC_INC(&foo) and
HA_ATOMIC_DEC(&foo) respectively. These are 507 changes over 45 files.
diff --git a/src/fcgi-app.c b/src/fcgi-app.c
index a1b6e68..2398709 100644
--- a/src/fcgi-app.c
+++ b/src/fcgi-app.c
@@ -474,12 +474,12 @@
 	goto end;
 
   rewrite_err:
-	_HA_ATOMIC_ADD(&sess->fe->fe_counters.failed_rewrites, 1);
-	_HA_ATOMIC_ADD(&s->be->be_counters.failed_rewrites, 1);
+	_HA_ATOMIC_INC(&sess->fe->fe_counters.failed_rewrites);
+	_HA_ATOMIC_INC(&s->be->be_counters.failed_rewrites);
 	if (sess->listener && sess->listener->counters)
-		_HA_ATOMIC_ADD(&sess->listener->counters->failed_rewrites, 1);
+		_HA_ATOMIC_INC(&sess->listener->counters->failed_rewrites);
 	if (objt_server(s->target))
-		_HA_ATOMIC_ADD(&__objt_server(s->target)->counters.failed_rewrites, 1);
+		_HA_ATOMIC_INC(&__objt_server(s->target)->counters.failed_rewrites);
   hdr_rule_err:
 	node = ebpt_first(&hdr_rules);
 	while (node) {