[base16] Add buffer size parameter to base16_encode() and base16_decode()

The current API for Base16 (and Base64) encoding requires the caller
to always provide sufficient buffer space.  This prevents the use of
the generic encoding/decoding functionality in some situations, such
as in formatting the hex setting types.

Implement a generic hex_encode() (based on the existing
format_hex_setting()), implement base16_encode() and base16_decode()
in terms of the more generic hex_encode() and hex_decode(), and update
all callers to provide the additional buffer length parameter.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/infiniband/ib_srp.c

@@ -291,7 +291,7 @@ static int ib_srp_parse_byte_string ( const char *rp_comp, uint8_t *bytes,
 		return -EINVAL_BYTE_STRING_LEN;
 
 	/* Parse byte string */
-	decoded_size = base16_decode ( rp_comp, bytes );
+	decoded_size = base16_decode ( rp_comp, bytes, size );
 	if ( decoded_size < 0 )
 		return decoded_size;