add more comments about bpfGetFd... and kernel version compatibility

Per request on:
  https://googleplex-android-review.googlesource.com/c/platform/frameworks/libs/net/+/18992756

Test: N/A
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I853d177623dc64fdac70ddefde3e0cc65d6b2c9a
1 file changed
tree: a5c159fbfc1ca48fb1722c05463c4b1595b01f5f
  1. staticlibs/