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>
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index b2cf91e..9d26a3d 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -407,7 +407,7 @@
 	  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).