route.h: introduce a macro, SA_SIZE(struct sockaddr *) which returns

route.h: introduce a macro, SA_SIZE(struct sockaddr *) which returns
the space occupied by a struct sockaddr when passed through a
routing socket.
Use it to replace the macro ROUNDUP(int), that does the same but
is redefined by every file which uses it, courtesy of
the School of Cut'n'Paste Programming(TM).

(partial) userland changes to follow.