package/irqbalance: fix sysv startup script (add mkdir /run/irqbalance)

package/irqbalance: fix sysv startup script (add mkdir /run/irqbalance)

- add mkdir -p /run/irqbalance to sysv startup script needed to
  create socket /run/irqbalance/irqbalance<pid>.sock

Fixes:

  - Bug 13541 [1]

  daemon.warn /usr/sbin/irqbalance: Daemon couldn't be bound to the file-based socket.

[1] https://bugs.busybox.net/show_bug.cgi?id=13541

Reported-by: Alfredo Pons Menargues <alfredo.pons@gmail.com>
Signed-off-by: Peter Seiderer <ps.report@gmx.net>
[yann.morin.1998@free.fr: only create in start case]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>