Wireless Wire MTU, stability

The plot thickens further.

On both current and rc builds, Wireless Wire has an issue at any MTU over 1704.

To replicate, set L2/L3 MTU on Wireless Wire eth1 and w60 interfaces to Nominal MTU. Send a packet through the bridge larger than Actual MTU, and the link will go down.

 Nominal MTU — Actual MTU — Differential in bytes
2290	2264	26
2284	2264	20
2276	2256	20
2264	2240	24
2024	2000	24
1812	1790	22
1758	1736	22
1732	1712	20
1720	1704	16
1712	1704	8
1706	1704	2
1704	1704	0