bpf: hostfw: use tailcall buffer for ipv{4,6}_host_policy_{e,in}gress - #47648

Similarly to what has been done in commit 524a591 ("bpf: Never
allocate ct_buffers on stack"), let's move the `ct_buffer` to a pointer
in `ipv{4,6}_host_policy_egress`. No additional code changes should be
needed, as we initialize and use fields in subsequent functions as long
as we need them.

This should free us some space in stack and lower complexity.

This requires moving the `cilium_tail_call_buffer{4,6}` map definitions
before we include host_firewall.h. In host_firewall.h we already gate
and protect to use it only when IS_BPF_HOST.

Signed-off-by: Simone Magnani <[email protected]>