bpf: Fix reStructuredText markup

The patch fixes:
$ scripts/bpf_helpers_doc.py > bpf-helpers.rst
$ rst2man bpf-helpers.rst > bpf-helpers.7
bpf-helpers.rst:1105: (WARNING/2) Inline strong start-string without end-string.
Signed-off-by: Jakub Wilk <jwilk@jwilk.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20200422082324.2030-1-jwilk@jwilk.net

include/uapi/linux/bpf.h

@@ -1642,7 +1642,7 @@ union bpf_attr {
  * 		ifindex, but doesn't require a map to do so.
  * 	Return
  * 		**XDP_REDIRECT** on success, or the value of the two lower bits
- * 		of the **flags* argument on error.
+ * 		of the *flags* argument on error.
  *
  * int bpf_sk_redirect_map(struct sk_buff *skb, struct bpf_map *map, u32 key, u64 flags)
  * 	Description

tools/include/uapi/linux/bpf.h

@@ -1642,7 +1642,7 @@ union bpf_attr {
  * 		ifindex, but doesn't require a map to do so.
  * 	Return
  * 		**XDP_REDIRECT** on success, or the value of the two lower bits
- * 		of the **flags* argument on error.
+ * 		of the *flags* argument on error.
  *
  * int bpf_sk_redirect_map(struct sk_buff *skb, struct bpf_map *map, u32 key, u64 flags)
  * 	Description