connmgr: Count unsent async messages. #1801

Job	Run time
osx clang --disable-ssl	4m 40s
linux gcc --disable-ssl	4m 8s
linux clang --disable-ssl	3m 47s
linux gcc test	12m 19s
linux clang test asan	18m 51s
linux clang test ubsan	14m 17s
linux gcc test --enable-shared	18m 48s
linux clang test --enable-shared	16m 56s
linux gcc test dpdk	12m 27s
linux clang test dpdk	10m 30s
linux gcc test -ljemalloc	12m 58s
linux clang test -ljemalloc	11m 45s
linux gcc afxdp 5.3	4m 13s
linux clang afxdp 5.3	4m 5s
linux gcc dpdk --enable-shared	4m 59s
linux clang dpdk --enable-shared	6m 6s
linux gcc dpdk-shared	3m 49s
linux clang dpdk-shared	3m 23s
linux gcc dpdk-shared --enable-shared	5m 9s
linux clang dpdk-shared --enable-shared	5m 20s
linux gcc m32 --disable-ssl	4m 7s
linux deb no dpdk	8m 43s
linux deb shared dpdk	17m 39s
	3h 28m 59s

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