Return UNKNOWN instead of CRITICAL on all SSL-layer problems

Plugin should behave consistently and report CRITICAL only when explicitly got from
remote side or remote side is completely down.

All other cases, when remote side is up, but we unable to get correct response - should
return UNKNOWN, like it was implemented for non-SSL connections.

src/check_nrpe.c

@@ -896,7 +896,7 @@ void setup_ssl()
 
 		if ((ctx = SSL_CTX_new(meth)) == NULL) {
 			printf("CHECK_NRPE: Error - could not create SSL context.\n");
-			exit(STATE_CRITICAL);
+			exit(timeout_return_code);
 		}
 
 #if OPENSSL_VERSION_NUMBER >= 0x10100000
@@ -976,7 +976,7 @@ void setup_ssl()
 					printf("Error: could not use certificate file '%s': %s\n", sslprm.cert_file, ERR_reason_error_string(x));
 				}
 				SSL_CTX_free(ctx);
-				exit(STATE_CRITICAL);
+				exit(timeout_return_code);
 			}
 			if (!SSL_CTX_use_PrivateKey_file(ctx, sslprm.privatekey_file, SSL_FILETYPE_PEM)) {
 				SSL_CTX_free(ctx);
@@ -985,7 +985,7 @@ void setup_ssl()
 					printf("Error: could not use private key file '%s': %s\n", sslprm.privatekey_file, ERR_reason_error_string(x));
 				}
 				SSL_CTX_free(ctx);
-				exit(STATE_CRITICAL);
+				exit(timeout_return_code);
 			}
 		}
 
@@ -998,7 +998,7 @@ void setup_ssl()
 					printf("Error: could not use CA certificate '%s': %s\n", sslprm.privatekey_file, ERR_reason_error_string(x));
 				}
 				SSL_CTX_free(ctx);
-				exit(STATE_CRITICAL);
+				exit(timeout_return_code);
 			}
 		}
 
@@ -1025,7 +1025,7 @@ void setup_ssl()
 				printf("Could not set SSL/TLS cipher list '%s': %s\n", sslprm.cipher_list, ERR_reason_error_string(x));
 			}
 			SSL_CTX_free(ctx);
-			exit(STATE_CRITICAL);
+			exit(timeout_return_code);
 		}
 	}
 #endif
@@ -1085,7 +1085,7 @@ int connect_to_remote()
 	/* do SSL handshake */
 	if ((ssl = SSL_new(ctx)) == NULL) {
 		printf("CHECK_NRPE: Error - Could not create SSL connection structure.\n");
-		return STATE_CRITICAL;
+		return timeout_return_code;
 	}
 
 	SSL_set_fd(ssl, sd);
@@ -1132,7 +1132,7 @@ int connect_to_remote()
 		 */
 		ERR_print_errors_fp(stdout);
 # endif
-		result = STATE_CRITICAL;
+		result = timeout_return_code;
 
 	} else {