bpf: one cannot compile BPFs that include rte_mbuf_core.h

A BPF needs to include the header `` to access `struct rte_mbuf`. But the current version of the header `` cannot be included in a BPF. This bug is present in the latest DPDK (i.e. 23.11) and a [bug report](https://bugs.dpdk.org/show_bug.cgi?id=1376) has been filed.

Here's the error one gets while compiling the BPFs included with Gatekeeper:
```
~/gatekeeper/bpf$ make
clang -O2 -g -target bpf -I../include -Wall -Wextra -Wno-int-to-void-pointer-cast -o granted.bpf -c granted.c
In file included from granted.c:29:
In file included from /usr/local/include/rte_mbuf_core.h:21:
/usr/local/include/rte_byteorder.h:31:16: error: invalid output constraint '=Q' in asm
: [x1] "=Q" (x)
^
1 error generated.
make: *** [Makefile:17: granted.bpf] Error 1
```