broadcom-wl: fix compilation with kernel >= 4.15

Since kernel 4.15, init_timer is not available anymore, and has been
replaced by timer_setup. The fixes compilation of wl_linuc.c, which
returned the following errors beforehand (line-wrapped manually):

.../broadcom-wl-5.10.56.27.3/driver/wl_linux.c: In function 'wl_init_timer':
.../broadcom-wl-5.10.56.27.3/driver/wl_linux.c:2576:2: error: implicit
	declaration of function 'init_timer'; did you mean 'init_timers'?
	[-Werror=implicit-function-declaration]
  init_timer(&t->timer);
  ^~~~~~~~~~
  init_timers
.../broadcom-wl-5.10.56.27.3/driver/wl_linux.c:2577:10: error:
	'struct timer_list' has no member named 'data'
  t->timer.data = (ulong) t;
          ^
.../broadcom-wl-5.10.56.27.3/driver/wl_linux.c:2578:20: error: assignment
	to 'void (*)(struct timer_list *)' from incompatible pointer type
	'void (*)(ulong)' {aka 'void (*)(long unsigned int)'}
	[-Werror=incompatible-pointer-types]
  t->timer.function = wl_timer;

This should fix build of several devices on bcm63xx with testing
kernel (4.19).

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

package/kernel/broadcom-wl/patches/915-fix-wl_timer-for-4_15.patch

@@ -0,0 +1,55 @@
+--- a/driver/wl_linux.c
++++ b/driver/wl_linux.c
+@@ -235,7 +235,11 @@
+ 
+ };
+ 
++#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 15, 0)
++static void wl_timer(struct timer_list *tl);
++#else
+ static void wl_timer(ulong data);
++#endif
+ static void _wl_timer(wl_timer_t *t);
+ 
+ #ifdef WLC_HIGH_ONLY
+@@ -2512,6 +2517,18 @@
+ }
+ #endif /* WLC_HIGH_ONLY */
+ 
++#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 15, 0)
++static void
++wl_timer(struct timer_list *tl)
++{
++	wl_timer_t *t = from_timer(t, tl, timer);
++#ifndef WLC_HIGH_ONLY
++	_wl_timer(t);
++#else
++	wl_schedule_task(t->wl, wl_timer_task, t);
++#endif /* WLC_HIGH_ONLY */
++}
++#else
+ static void
+ wl_timer(ulong data)
+ {
+@@ -2522,6 +2539,7 @@
+ 	wl_schedule_task(t->wl, wl_timer_task, t);
+ #endif /* WLC_HIGH_ONLY */
+ }
++#endif /* linux >= 4.15.0 */
+ 
+ static void
+ _wl_timer(wl_timer_t *t)
+@@ -2573,9 +2591,13 @@
+ 
+ 	bzero(t, sizeof(wl_timer_t));
+ 
++#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 15, 0)
++	timer_setup(&t->timer, wl_timer, 0);
++#else
+ 	init_timer(&t->timer);
+ 	t->timer.data = (ulong) t;
+ 	t->timer.function = wl_timer;
++#endif
+ 	t->wl = wl;
+ 	t->fn = fn;
+ 	t->arg = arg;