MI: add command timeouts

[jk-ozlabs]

This series implements a facility for endpoint-specific timeouts for the NVMe-MI transports. We add a simple API to get/set timeout values:

/**
 * nvme_mi_ep_set_timeout - set a timeout for NVMe-MI responses
 * @ep: MI endpoint object
 * @timeout_ms: Timeout for MI responses, given in milliseconds
 */
int nvme_mi_ep_set_timeout(nvme_mi_ep_t ep, unsigned int timeout_ms);

/**
 * nvme_mi_ep_set_mprt_max - set the maximum wait time for a More Processing
 * Required response
 * @ep: MI endpoint object
 * @mprt_max_ms: Maximum more processing required wait time
 *
 * NVMe-MI endpoints may respond to a request with a "More Processing Required"
 * response; this also includes a hint on the worst-case processing time for
 * the eventual response data, with a specification-defined maximum of 65.535
 * seconds.
 *
 * This function provides a way to limit the maximum time we're prepared to
 * wait for the final response. Specify zero in @mprt_max_ms for no limit.
 * This should be larger than the command/response timeout set in
 * &nvme_mi_ep_set_timeout().
 */
void nvme_mi_ep_set_mprt_max(nvme_mi_ep_t ep, unsigned int mprt_max_ms);

/**
 * nvme_mi_ep_get_timeout - get the current timeout value for NVMe-MI responses
 * @ep: MI endpoint object
 *
 * Returns the current timeout value, in milliseconds, for this endpoint.
 */
unsigned int nvme_mi_ep_get_timeout(nvme_mi_ep_t ep);

- and implement this for the MCTP transport layer, plus a bunch of tests.

This means that we can recover from device/transport/address errors, instead of potentially blocking forever waiting for a response.

[codecov-commenter]

Codecov Report

Merging #432 (6a08780) into master (6c5aedd) will increase coverage by 1.75%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #432      +/-   ##
==========================================
+ Coverage   16.43%   18.19%   +1.75%     
==========================================
  Files          31       31              
  Lines        5068     5206     +138     
  Branches      973      997      +24     
==========================================
+ Hits          833      947     +114     
- Misses       3982     3988       +6     
- Partials      253      271      +18     

Impacted Files	Coverage Δ
src/nvme/mi.h	36.84% <ø> (ø)
src/nvme/mi.c	52.23% <61.53%> (+0.29%)	⬆️
src/nvme/mi-mctp.c	71.03% <80.76%> (+0.63%)	⬆️
test/mi-mctp.c	83.96% <86.66%> (+1.80%)	⬆️

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