ctl_report_supported_opcodes: Handle invalid requested service action

Service actions are only valid up to 31 as they are encoded in the low
5 bits of byte 1 in CDBs. Fail requests with a requested service
action of 32 or higher with an INVALID FIELD IN COMMAND specifying
byte 4 as the illegal byte.

Reviewed by: asomers
Differential Revision: https://reviews.freebsd.org/D46611