xfrm: make xfrm_alg_len() return unsigned int

Key lengths can't be negative.

Comparison with nla_len() is left signed just in case negative value
can sneak in there.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 0be4c54..2abc0e1 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1769,7 +1769,7 @@
 	return sizeof(*alg) + ((alg->alg_key_len + 7) / 8);
 }
 
-static inline int xfrm_alg_len(const struct xfrm_algo *alg)
+static inline unsigned int xfrm_alg_len(const struct xfrm_algo *alg)
 {
 	return sizeof(*alg) + ((alg->alg_key_len + 7) / 8);
 }