sparse: Include stddef.h to ensure NULL is defined.

Include stddef.h in include/sparse/sys/socket.h to ensure
that NULL is defined and thus avoid the following sparse warning.

./include/sparse/sys/socket.h:74:15: error: undefined identifier 'NULL'

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Avoid printf type modifiers not supported by MSVC C runtime library.

The MSVC C library printf() implementation does not support the 'z', 't',
'j', or 'hh' format specifiers.  This commit changes the Open vSwitch code
to avoid those format specifiers, switching to standard macros from
<inttypes.h> where available and inventing new macros resembling them
where necessary.  It also updates CodingStyle to specify the macros' use
and adds a Makefile rule to report violations.

Signed-off-by: Alin Serdean <aserdean@cloudbasesolutions.com>
Co-authored-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>