tsleep_nsec(9) for revarp

[Martin Pieuchot]

The hz/2 idiom means 500ms, so use that.  ok?

Index: netinet/if_ether.c
===================================================================
RCS file: /cvs/src/sys/netinet/if_ether.c,v
retrieving revision 1.240
diff -u -p -r1.240 if_ether.c
--- netinet/if_ether.c  17 Jul 2019 16:46:18 -0000      1.240
+++ netinet/if_ether.c  7 Oct 2019 12:49:44 -0000
@@ -914,7 +914,7 @@ revarpwhoarewe(struct ifnet *ifp, struct
        revarp_ifidx = ifp->if_index;
        while (count--) {
                revarprequest(ifp);
-               result = tsleep((caddr_t)&revarp_myip, PSOCK, "revarp", hz/2);
+               result = tsleep_nsec(&revarp_myip, PSOCK, "revarp", 
MSEC_TO_NSEC(500));
                if (result != EWOULDBLOCK)
                        break;
        }