Add OFB ciphers to EVP_get_cipherbyname.

This is so they're exposed out of cryptography.io.

Change-Id: I225a35605ae8f3da091e95241ce072eeeabcd855
Reviewed-on: https://boringssl-review.googlesource.com/29044
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/crypto/cipher_extra/cipher_extra.c b/crypto/cipher_extra/cipher_extra.c
index e770489..2b88fb6 100644
--- a/crypto/cipher_extra/cipher_extra.c
+++ b/crypto/cipher_extra/cipher_extra.c
@@ -123,6 +123,10 @@
     return EVP_aes_192_gcm();
   } else if (OPENSSL_strcasecmp(name, "aes-256-gcm") == 0) {
     return EVP_aes_256_gcm();
+  } else if (OPENSSL_strcasecmp(name, "aes-128-ofb") == 0) {
+    return EVP_aes_128_ofb();
+  } else if (OPENSSL_strcasecmp(name, "aes-256-ofb") == 0) {
+    return EVP_aes_256_ofb();
   }
 
   return NULL;