KeyboardSettings+Kernel: Setting to enable Num Lock on login

Author: https://github.com/ForLoveOfCats
Commit: ce6658acc1
Pull-request: https://github.com/SerenityOS/serenity/pull/8417
Reviewed-by: https://github.com/gunnarbeutner

Kernel/API/Syscall.h

@@ -143,6 +143,7 @@ namespace Kernel {
     S(getrandom)                  \
     S(getkeymap)                  \
     S(setkeymap)                  \
+    S(set_num_lock)               \
     S(clock_gettime)              \
     S(clock_settime)              \
     S(clock_nanosleep)            \