Protection Type support for 4 bit checksums

[nickumlauf]

my check sum is 4 bits and it looks like this custom device checksum is calculated for u8.
the formula we use is
Chksum = (Byte1 + (Byte2 & 0x0F) + Byte3 + Byte4 + Byte5 + Byte6 + Byte7 + Bytes8 + msgID byte1 + msgID byte2 + msgID byte3 + msgID byte4)
= (((chksum >> 6) & 0x03) + (chksum >>3) + chksum) & 0x07
= ((chksum & 0x0F) << 4) + (chksum & 0x0F)

would it be possible to add an option to make for 4 bit checksum:
chksum = "Arb ID + Bytes Checksum with Inversion"
= (((chksum >> 6) & 0x03) + (chksum >>3) + chksum) & 0x07

please build for Veristand 2017