sock: introduce SO_MEMINFO getsockopt

Allows reading of SK_MEMINFO_VARS via socket option. This way an
application can get all meminfo related information in single socket
option call instead of multiple calls.

Adds helper function, sk_get_meminfo(), and uses that for both
getsockopt and sock_diag_put_meminfo().

Suggested by Eric Dumazet.

Signed-off-by: Josh Hunt <johunt@akamai.com>
Reviewed-by: Jason Baron <jbaron@akamai.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index a25dc32..12cd8c2 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -88,6 +88,8 @@
 
 #define SCM_TIMESTAMPING_OPT_STATS	0x0038
 
+#define SO_MEMINFO		0x0039
+
 /* Security levels - as per NRL IPv6 - don't actually do anything */
 #define SO_SECURITY_AUTHENTICATION		0x5001
 #define SO_SECURITY_ENCRYPTION_TRANSPORT	0x5002