crypto: echainiv - Set Kconfig default to m

As this is required by many IPsec algorithms, let's set the default
to m.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -244,6 +244,7 @@ config CRYPTO_ECHAINIV
 	select CRYPTO_AEAD
 	select CRYPTO_NULL
 	select CRYPTO_RNG
+	default m
 	help
 	  This IV generator generates an IV based on the encryption of
 	  a sequence number xored with a salt.  This is the default