samples/bpf: add -Wno-unknown-warning-option to clang
I was initially going to remove '-Wno-address-of-packed-member' because I
thought it was not supposed to be there but Daniel suggested using
'-Wno-unknown-warning-option'.
This silences several warnings similiar to the one below
Signed-off-by: Alexander Alemayhu <alexander@alemayhu.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>