bpf tcp save syn set/get sockoptions

adding supprot for two new bpf's tcp sockopts:
TCP_SAVE_SYN (set) and TCP_SAVED_SYN (get)
this would allow for tcp-bpf program to build some logic based on fields from ingress syn packet (e.g. doing tcp's tos/tclass reflection (see sample prog)) and do it transparently from userspace program point of view

v2->v3:
- make patch series public
v1->v2:
- adding proper SPDX license

Nikita V. Shirokov (2):
new options for bpf_(set|get)sockopt
new sample bpf prog

 net/core/filter.c                  | 25 +++++++--
 samples/bpf/Makefile               |  1 +
 samples/bpf/tcp_tos_reflect_kern.c | 87 ++++++++++++++++++++++++++++++
 3 files changed, 109 insertions(+), 4 deletions(-)
 create mode 100644 samples/bpf/tcp_tos_reflect_kern.c

2.17.1