tools: bpftool: Log info-level messages when building bpftool man pages

To build man pages for bpftool (and for eBPF helper functions), rst2man
can log different levels of information. Let's make it log all levels
to keep the RST files clean.

Doing so, rst2man complains about double colons, used for literal
blocks, that look like underlines for section titles. Let's add the
necessary blank lines.

v2:
- Use "--verbose" instead of "-r 1" (same behaviour but more readable).
- Pass it through a RST2MAN_OPTS variable so we can easily pass other
options too.

Signed-off-by: Quentin Monnet <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/bpf/bpftool/Documentation/Makefile

···
 man8: $(DOC_MAN8)
 
 RST2MAN_DEP := $(shell command -v rst2man 2>/dev/null)
+RST2MAN_OPTS += --verbose
 
 $(OUTPUT)%.8: %.rst
 ifndef RST2MAN_DEP
 	$(error "rst2man not found, but required to generate man pages")
 endif
-	$(QUIET_GEN)rst2man $< > $@
+	$(QUIET_GEN)rst2man $(RST2MAN_OPTS) $< > $@
 
 clean: helpers-clean
 	$(call QUIET_CLEAN, Documentation)

tools/bpf/bpftool/Documentation/bpftool-btf.rst

···
 EXAMPLES
 ========
 **# bpftool btf dump id 1226**
+
 ::
 
   [1] PTR '(anon)' type_id=2
···
 This gives an example of default output for all supported BTF kinds.
 
 **$ cat prog.c**
+
 ::
 
   struct fwd_struct;
···
   }
 
 **$ bpftool btf dump file prog.o**
+
 ::
 
   [1] PTR '(anon)' type_id=2

tools/bpf/bpftool/Documentation/bpftool-gen.rst

···
 EXAMPLES
 ========
 **$ cat example.c**
+
 ::
 
   #include <stdbool.h>
···
 and global variables.
 
 **$ bpftool gen skeleton example.o**
+
 ::
 
   /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
···
   #endif /* __EXAMPLE_SKEL_H__ */
 
 **$ cat example_user.c**
+
 ::
 
   #include "example.skel.h"
···
   }
 
 **# ./example_user**
+
 ::
 
   my_map name: my_map

tools/bpf/bpftool/Documentation/bpftool-map.rst

···
 EXAMPLES
 ========
 **# bpftool map show**
+
 ::
 
   10: hash  name some_map  flags 0x0
···
 
 
 **# bpftool map dump id 10**
+
 ::
 
   key: 00 01 02 03  value: 00 01 02 03 04 05 06 07
···
   Found 2 elements
 
 **# bpftool map getnext id 10 key 0 1 2 3**
+
 ::
 
   key: