mavlink_stream: mutex lock for register/unregister poll #1432

Job	Run time
variables	1s
fc_matrix (pixhawk) / build	6m 1s
fc_matrix (fmu-v6xrt) / build	6m 43s
fc_matrix (saluki-nxp93_flat) / build	5m 27s
fc_matrix (saluki-pi_amp) / build	8m 51s
fc_matrix (saluki-pi_custom_keys, Tools/saluki-sec-scripts/custom_keys/saluki-pi/px4_bin_ed25519_... / build	8m 48s
fc_matrix (saluki-pi_default) / build	8m 48s
fc_matrix (saluki-pi_flat) / build	6m 38s
fc_matrix (saluki-v2_amp) / build	9m 23s
fc_matrix (saluki-v2_custom_keys, Tools/saluki-sec-scripts/custom_keys/saluki-v2/px4_bin_ed25519_... / build	9m 21s
fc_matrix (saluki-v2_default) / build	8m 53s
fc_matrix (saluki-v2_flat) / build	7m 5s
fc_matrix (saluki-v3_amp) / build	8m 44s
fc_matrix (saluki-v3_custom_keys, Tools/saluki-sec-scripts/custom_keys/saluki-v3/px4_bin_ed25519_... / build	8m 48s
fc_matrix (saluki-v3_default) / build	9m 6s
fc_matrix (saluki-v3_flat) / build	6m 39s
build px4fwupdater	3m 20s
upload px4fwupdater to docker registry	1m 27s
upload builds to UAE artifactory	3m 28s
upload px4fwupdater to UAE docker registry	0s
	2h 7m 31s

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