ip: officially support flag mngtmpaddr also for "ip addr del"

Kernel is being extended to support flag IFA_F_MANAGETEMPADDR also for
deletion of addresses. This will allow a userspace application to indicate
that for a global address the kernel should delete all related temporary
addresses as well.

"ip addr del" internally calls ipaddr_modify which silently accepts
any flag provided on the command line already, independent of the
actual command.
Therefore only the usage documentation needs to be extended.

Signed-off-by: Heiner Kallweit <heiner.kallweit@web.de>
diff --git a/ip/ipaddress.c b/ip/ipaddress.c
index e3be5b2..8169150 100644
--- a/ip/ipaddress.c
+++ b/ip/ipaddress.c
@@ -69,7 +69,7 @@
 	}
 	fprintf(stderr, "Usage: ip addr {add|change|replace} IFADDR dev STRING [ LIFETIME ]\n");
 	fprintf(stderr, "                                                      [ CONFFLAG-LIST ]\n");
-	fprintf(stderr, "       ip addr del IFADDR dev STRING\n");
+	fprintf(stderr, "       ip addr del IFADDR dev STRING [mngtmpaddr]\n");
 	fprintf(stderr, "       ip addr {show|save|flush} [ dev STRING ] [ scope SCOPE-ID ]\n");
 	fprintf(stderr, "                            [ to PREFIX ] [ FLAG-LIST ] [ label PATTERN ] [up]\n");
 	fprintf(stderr, "       ip addr {showdump|restore}\n");