net: lib: coap: coap_packet_parse() returns different error values

coap_packet_parse() returns different values depending on error.
It now returns
-EINVAL for invalid input arguments,
-EBADMSG for malformed coap header,
-EILSEQ for malformed options error.

Fixes: #48960

Signed-off-by: Sagar Shah <sagar.shah@legrand.us>