Support proxy SRT media server. #1683

Job	Run time
multiple-arch-armv7	22m 15s
multiple-arch-aarch64	22m 35s
cygwin64-cache	1m 53s
utest-regression-blackbox-test	9m 36s
cygwin64	13m 45s
fast	1s
build-cross-aarch64	5m 7s
build-cross-arm	5m 12s
build-ubuntu16	3m 3s
build-centos7	4m 57s
build-ubuntu18	3m 12s
build-ubuntu20	3m 31s
coverage	3m 37s
multiple-arch-amd64	2m 18s
test-done	1s
	1h 41m 3s

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