mbedtls: send close-notify on close #1

Job	Run time
cygwin (automake, x86_64, --enable-debug --disable-threaded-resolver)	28m 59s
cygwin (cmake, x86_64, -DCURL_USE_OPENSSL=ON)	3m 37s
msys2 (autotools, msys, x86_64, --enable-debug --disable-threaded-resolver --disable-proxy)	16m 17s
msys2 (autotools, msys, x86_64, --enable-debug --disable-threaded-resolver)	16m 55s
msys2 (autotools, msys, x86_64, )	12m 47s
msys2 (cmake, mingw64, x86_64, -DENABLE_DEBUG=ON -DBUILD_SHARED_LIBS=OFF -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON)	8m 41s
msys2 (cmake, mingw64, x86_64, -DENABLE_DEBUG=ON -DBUILD_SHARED_LIBS=OFF -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON)	6m 15s
msys2 (cmake, clang64, clang-x86_64, -DENABLE_DEBUG=ON -DBUILD_SHARED_LIBS=OFF -DCURL_USE_OPENSSL=ON -DENABLE_UNICODE=OFF)	4m 51s
	1h 38m 22s

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