SCTP: Fix build issues with SCTP AUTH.

SCTP-AUTH requires selection of CRYPTO, HMAC and SHA1 since
SHA1 is a MUST requirement for AUTH.  We also support SHA256,
but that's optional, so fix the code to treat it as such.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index 6d89e35..97e6ebd 100644
--- a/net/sctp/auth.c
+++ b/net/sctp/auth.c
@@ -54,11 +54,13 @@
 		/* id 2 is reserved as well */
 		.hmac_id = SCTP_AUTH_HMAC_ID_RESERVED_2,
 	},
+#if defined (CONFIG_CRYPTO_SHA256) || defined (CONFIG_CRYPTO_SHA256_MODULE)
 	{
 		.hmac_id = SCTP_AUTH_HMAC_ID_SHA256,
 		.hmac_name="hmac(sha256)",
 		.hmac_len = SCTP_SHA256_SIG_SIZE,
 	}
+#endif
 };