ip/ipreassembler: fix positive header_delta push path

[pallas]

Like the put earlier in this method, the push here can fail or reallocate the SKB. In the former case, we need to clean up (as above) and in both cases, we need to update the linkage into q from it's predecessor.

Thanks: --enable-force-expensive + Valgrind

Signed-off-by: Derrick Pallas [email protected]