ib/ipoib: Fix removing call for update_pmtu from spin-lock context.

ib/ipoib: Fix removing call for update_pmtu from spin-lock context.

    The function ipoib_cm_send can call the function
    ipoib_cm_skb_too_long under spin_lock_irq, the
    ipoib_cm_skb_too_long function calls update_pmtu which also
    tries to get spin_lock, that can cause to a deadlock.
    In order to solve that I took update_pmtu to workqueue that
    it is not under spin_lock.

V2: Adjusted for kernel 3.7-rc4

Signed-off-by: Erez Shitrit <erezsh@mellanox.com>
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
(Ported from Mellanox OFED 2.4)

Signed-off-by: Mukesh Kacker <mukesh.kacker@oracle.com>