bpf: sockmap requires STREAM_PARSER add Kconfig entry

SOCKMAP uses strparser code (compiled with Kconfig option
CONFIG_STREAM_PARSER) to run the parser BPF program. Without this
config option set sockmap wont be compiled. However, at the moment
the only way to pull in the strparser code is to enable KCM.

To resolve this create a BPF specific config option to pull
only the strparser piece in that sockmap needs. This also
allows folks who want to use BPF/syscall/maps but don't need
sockmap to easily opt out.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>