Some manual pages are already using C99 syntax for integral
types 'uint32_t', but some aren't.  There are some using kernel
syntax '__u32'.  Fix those.

Some pages also document attributes, using GNU syntax
'__attribute__((xxx))'.  Update those to use the shorter and more
portable C11 keywords such as 'alignas()' when possible, and C2x
syntax '[[gnu::xxx]]' elsewhere, which hasn't been standardized
yet, but is already implemented in GCC, and available through
either --std=c2x or any of the --std=gnu... options.

The standard isn't very clear on how to use alignas() or
[[]]-style attributes, so the following link is useful in the case
of 'alignas()' and '[[gnu::aligned()]]':
<https://stackoverflow.com/q/67271825/6872717>

Signed-off-by: Alejandro Colomar <redacted>
Cc: LKML <redacted>
Cc: glibc <redacted>
Cc: GCC <redacted>
Cc: Alexei Starovoitov <redacted>
Cc: bpf <redacted>
Cc: David Laight <redacted>
Cc: Zack Weinberg <redacted>
Cc: Joseph Myers <redacted>
---
 man2/bpf.2 | 49 ++++++++++++++++++++++++-------------------------
 1 file changed, 24 insertions(+), 25 deletions(-)

diff --git a/man2/bpf.2 b/man2/bpf.2
index 6e1ffa198..04b8fbcef 100644
--- a/man2/bpf.2
+++ b/man2/bpf.2

@@ -186,41 +186,40 @@ commands:
 .PP
 .in +4n
 .EX
-union bpf_attr {
+union [[gnu::aligned(8)]] bpf_attr {
     struct {    /* Used by BPF_MAP_CREATE */
-        __u32         map_type;
-        __u32         key_size;    /* size of key in bytes */
-        __u32         value_size;  /* size of value in bytes */
-        __u32         max_entries; /* maximum number of entries
-                                      in a map */
+        uint32_t    map_type;
+        uint32_t    key_size;    /* size of key in bytes */
+        uint32_t    value_size;  /* size of value in bytes */
+        uint32_t    max_entries; /* maximum number of entries
+                                    in a map */