This patch adds a bpf self-test to cover BPF_LWT_ENCAP_IP mode
in bpf_lwt_push_encap.

Covered:
- encapping in LWT_IN and LWT_XMIT
- IPv4 and IPv6

A follow-up patch will add GSO and VRF-enabled tests.

Signed-off-by: Peter Oskolkov <redacted>
---
 tools/testing/selftests/bpf/Makefile          |   5 +-
 .../testing/selftests/bpf/test_lwt_ip_encap.c |  85 +++++
 .../selftests/bpf/test_lwt_ip_encap.sh        | 311 ++++++++++++++++++
 3 files changed, 399 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/test_lwt_ip_encap.c
 create mode 100755 tools/testing/selftests/bpf/test_lwt_ip_encap.sh

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index c7e1e3255448..3ebd41a0c253 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile

@@ -36,7 +36,7 @@ BPF_OBJ_FILES = \
 	get_cgroup_id_kern.o socket_cookie_prog.o test_select_reuseport_kern.o \
 	test_skb_cgroup_id_kern.o bpf_flow.o netcnt_prog.o test_xdp_vlan.o \
 	xdp_dummy.o test_map_in_map.o test_spin_lock.o test_map_lock.o \
-	test_sock_fields_kern.o
+	test_sock_fields_kern.o test_lwt_ip_encap.o