Update expressroute-faqs.md

update MTU

Author: carlost-MSFT

articles/expressroute/expressroute-faqs.md

@@ -154,7 +154,7 @@ Supported bandwidth offers:
 
 ### What's the maximum MTU supported?
 
-ExpressRoute supports the standard internet MTU of 1400 bytes.
+ExpressRoute supports the standard internet MTU of 1500 bytes.
 See [TCP/IP performance tuning for Azure VMs](../virtual-network/virtual-network-tcpip-performance-tuning.md) for tuning the MTU of your VMs.
 
 ### Which service providers are available?