ipv4: Make INET_LRO a bool instead of tristate.

This code is used as a library by several device drivers,
which select INET_LRO.

If some are modules and some are statically built into the
kernel, we get build failures if INET_LRO is modular.
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/Kconfig

@@ -407,7 +407,7 @@ config INET_XFRM_MODE_BEET
 	  If unsure, say Y.
 
 config INET_LRO
-	tristate "Large Receive Offload (ipv4/tcp)"
+	bool "Large Receive Offload (ipv4/tcp)"
 
 	---help---
 	  Support for Large Receive Offload (ipv4/tcp).