REORG: threads: move all_thread_mask() to thread.h

It was declared in global.h, forcing plenty of source files to include
it only for this while it's only based on definitions from thread.h.
diff --git a/include/haproxy/global.h b/include/haproxy/global.h
index 1c50aba..547a2b8 100644
--- a/include/haproxy/global.h
+++ b/include/haproxy/global.h
@@ -89,12 +89,6 @@
 	return mask ? mask : all_proc_mask;
 }
 
-/* returns a mask if set, otherwise all_threads_mask */
-static inline unsigned long thread_mask(unsigned long mask)
-{
-	return mask ? mask : all_threads_mask;
-}
-
 /* handle 'tainted' status */
 enum tainted_flags {
 	TAINTED_CONFIG_EXP_KW_DECLARED = 0x1,
diff --git a/include/haproxy/thread.h b/include/haproxy/thread.h
index 6a4b400..d158027 100644
--- a/include/haproxy/thread.h
+++ b/include/haproxy/thread.h
@@ -969,4 +969,10 @@
 
 #endif /* USE_THREAD */
 
+/* returns a mask if set, otherwise all_threads_mask */
+static inline unsigned long thread_mask(unsigned long mask)
+{
+	return mask ? mask : all_threads_mask;
+}
+
 #endif /* _HAPROXY_THREAD_H */