Rename *KEYPAIR* to *KEY_PAIR*

Be consistent with PUBLIC_KEY.

perl -i -pe 's/KEYPAIR/KEY_PAIR/g' $(git ls-files)
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 41c2bd2..cde368f 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -3149,7 +3149,7 @@
 
         /* Generate ECDH private key. */
         status = psa_generate_random_key_to_handle( handshake->ecdh_psa_privkey,
-                          PSA_KEY_TYPE_ECC_KEYPAIR( handshake->ecdh_psa_curve ),
+                          PSA_KEY_TYPE_ECC_KEY_PAIR( handshake->ecdh_psa_curve ),
                           MBEDTLS_PSA_ECC_KEY_BITS_OF_CURVE( handshake->ecdh_psa_curve ),
                           NULL, 0 );
         if( status != PSA_SUCCESS )