don't use a bogus pointer if packblock reallocates

Reference: /n/atom/patch/applied/nixetherusbpack
Date: Sun Jan  3 03:17:52 CET 2016
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/etherusb.c	Sun Jan  3 03:17:07 2016
+++ /sys/src/nix/k10/etherusb.c	Sun Jan  3 03:17:08 2016
@@ -125,7 +125,7 @@
 static int
 unpackasix(Ether *edev, Block *b)
 {
-	ulong hd;
+	u32int hd;
 	int m;
 	uchar *wp;
 
@@ -148,7 +148,7 @@
 static int
 unpacksmsc(Ether *edev, Block *b)
 {
-	ulong hd;
+	u32int hd;
 	int m;
 	
 	ddump('@', b);
@@ -198,10 +198,10 @@
 
 	n = BLEN(b) & 0xFFFF;
 	n |= ~n << 16;
-	padblock(b, 4);
+	b = padblock(b, 4);
 	PUT4(b->rp, n);
 	if(BLEN(b) % ctlr->maxpkt == 0){
-		padblock(b, -4);
+		b = padblock(b, -4);
 		PUT4(b->wp, 0xFFFF0000);
 		b->wp += 4;
 	}
@@ -214,7 +214,7 @@
 	int n;
 
 	n = BLEN(b) & 0x7FF;
-	padblock(b, 8);
+	b = padblock(b, 8);
 	PUT4(b->rp, n | SmscTxfirst | SmscTxlast);
 	PUT4(b->rp+4, n);
 	transmit(ctlr, b);
@@ -320,7 +320,7 @@
 }
 
 static long
-etherusbifstat(Ether* edev, void* a, long n, ulong offset)
+etherusbifstat(Ether* edev, void* a, long n, usize offset)
 {
 	char *s, *p, *e;
 	Ctlr *ctlr;
@@ -411,6 +411,11 @@
 	ctlr->edev = edev;
 }
 
+static void
+etherusbshutdown(Ether*)
+{
+}
+
 static int
 etherusbpnp(Ether* edev)
 {
@@ -429,6 +434,7 @@
 	edev->transmit = etherusbtransmit;
 	edev->ifstat = etherusbifstat;
 	edev->ctl = etherusbctl;
+	edev->shutdown = etherusbshutdown;
 	return 0;
 }