ath10k: sdio: remove skb_trim in TX path

This patch fixes a bug with padding of the skb data buffer.
Since skb_trim can only be used to reduce the skb len, it is useless when
we pad (increase the length of) the skb. Instead we allocate a new
buffer with enough space to contain both the TX data and padding.

Since some skb's have multiple references, we can't use skb_put_padto()
to extend and pad skb->data (since it causes a panic if there is more
than one reference).

Also, in order to avoid the following possible deadlock issue (reported by
lockdep):

[   26.508508]  Possible interrupt unsafe locking scenario:
[   26.508508]
[   26.515314]        CPU0                    CPU1
[   26.519862]        ----                    ----
[   26.524408]   lock(fs_reclaim);
[   26.527573]                                local_irq_disable();
[   26.533508]                                lock(_xmit_ETHER#2);
[   26.539453]                                lock(fs_reclaim);
[   26.545135]   <Interrupt>
[   26.547769]     lock(_xmit_ETHER#2);
[   26.551370]
[   26.551370]  *** DEADLOCK ***

... we use the GFP_NOFS flag with kzalloc()

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Patchwork-Id: 10906011
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>