perf: use reflect to test equity of message headers

[Aden-Q]

This patch uses reflection to test equality of message headers. This apporach is more efficient in the case when:

• Both m.Header and msg.Header are non-nil
• m.Header and msg.Header share the same underlying object, so the equality can be caught before testing the content of the map, compared to the original approach. For reference, map reflect implementation in go source code:

	case Map:
		if v1.IsNil() != v2.IsNil() {
			return false
		}
		if v1.Len() != v2.Len() {
			return false
		}
		if v1.UnsafePointer() == v2.UnsafePointer() {
			return true
		}
		iter := v1.MapRange()
		for iter.Next() {
			val1 := iter.Value()
			val2 := v2.MapIndex(iter.Key())
			if !val1.IsValid() || !val2.IsValid() || !deepValueEqual(val1, val2, visited) {
				return false
			}
		}
		return true