USB: gadget: u_bam: Fix out of order packet write to IPA/BAM_DMUX

Commit 613fdf2d (USB: gadget: u_bam: Avoid extra context switch
possibility in UL) introduces possibility of gbam_data_writeto_bam()
getting called concurrently. Though this function is protected well
with spin_lock to deal with this, but it may still end up sending
packets out of order to BAM_DMUX or IPA. This is possible if
one thread got preempted right after dequeuing the sk_buff and
before push it up.

Change-Id: Idb386a037a29d42b1817040273b5d717e6d439a5
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>