generic: drop 616-net_optimize_xfrm_calls.patch

generic: drop 616-net_optimize_xfrm_calls.patch

The conditional check introduced by this patch may trigger a NULL pointer
dereference in case the result of dev_net() is NULL.

Since the purpose of this patch is neither sufficiently explained and since
this patch apparently has never been submitted upstream despite it being in
the pending-* patch directory, I propose to drop it without replacement.

If the performance implications of dropping this patch are found to be
significiant, it should be reintroduced with proper description and
benchmark results.

Ref: https://bugs.openwrt.org/index.php?do=details&task_id=2943
Signed-off-by: Jo-Philipp Wich <jo@mein.io>