bpf: Fix two typos in uapi/linux/bpf.h

Also remove trailing whitespaces in bpf_skb_get_tunnel_key example code.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200821133642.18870-1-tklauser@distanz.ch