rmnet_core: Pass correct size to skb_copy_bits

When copying the QMAP header during deaggregation, the size of the data
to copy was incorrectly passed to skb_copy_bits() as the size of the
pointer instead of the struct. This lead to copying more data onto the
stack than there was room for.

Change-Id: I19208a8df2d8ce25a22fff95b71f1c56dcddec89
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>