MINOR: global: add option to disable numa detection

Render numa detection optional with a global configuration statement
'no numa-cpu-mapping'. This can be used if the applied affinity of the
algorithm is not optimal. Also complete the documentation with this new
keyword.

src/haproxy.c

@@ -160,6 +160,7 @@ volatile unsigned long stopping_thread_mask = 0; /* Threads acknowledged stoppin
 struct global global = {
 	.hard_stop_after = TICK_ETERNITY,
 	.nbproc = 1,
+	.numa_cpu_mapping = 1,
 	.nbthread = 0,
 	.req_count = 0,
 	.logsrvs = LIST_HEAD_INIT(global.logsrvs),