nforce: Disable MTU changes.

Strange KDLs showed up on at least one system with this driver after
the enabling of jumbo frames, so it seems probable that was the cause.
Disable MTU changes to hopefully prevent this problem for now.

Should hopefully stop #17766.

src/add-ons/kernel/drivers/network/ether/nforce/dev/nfe/if_nfe.c

@@ -1722,6 +1722,7 @@ nfe_ioctl(if_t ifp, u_long cmd, caddr_t data)
 	error = 0;
 	init = 0;
 	switch (cmd) {
+#ifndef __HAIKU__
 	case SIOCSIFMTU:
 		if (ifr->ifr_mtu < ETHERMIN || ifr->ifr_mtu > NFE_JUMBO_MTU)
 			error = EINVAL;
@@ -1741,6 +1742,7 @@ nfe_ioctl(if_t ifp, u_long cmd, caddr_t data)
 			}
 		}
 		break;
+#endif
 	case SIOCSIFFLAGS:
 		NFE_LOCK(sc);
 		if (if_getflags(ifp) & IFF_UP) {