IPS-157 Revert "No need for isErrorStatusCode"

This reverts commit 4bf16abe2e.

src/Util/PEPTransportStatusCodeUtil.h

@@ -17,6 +17,11 @@ NS_ASSUME_NONNULL_BEGIN
 /// @retun The severity octet of the given status code.
 + (NSUInteger)severityFromStatusCode:(PEPTransportStatusCode)statusCode;
 
+/// Is the given status code an error?
+/// @note A transport emitting this is supposed to "heal itself".
+/// @return `YES` if  the given status code is an error, `NO` if it isn't.
++ (BOOL)isErrorStatusCode:(PEPTransportStatusCode)statusCode;
+
 /// Is the given status code a critical error?
 /// @note A transport emitting this is _not_ supposed to be able to "heal itself".
 /// @return `YES` if  the given status code is a critical error, `NO` if it isn't.

src/Util/PEPTransportStatusCodeUtil.m

@@ -13,6 +13,10 @@
     return (statusCode >> 16) & 0xff;
 }
 
++ (BOOL)isErrorStatusCode:(PEPTransportStatusCode)statusCode {
+    return [self severityFromStatusCode:statusCode] == 0x80;
+}
+
 + (BOOL)isCriticalErrorStatusCode:(PEPTransportStatusCode)statusCode {
     return [self severityFromStatusCode:statusCode] == 0xff;
 }