tunnel: Do not carry source port from a previous tunnel. #2406

Job	Run time
osx clang --disable-ssl	2m 51s
linux gcc --disable-ssl	2m 8s
linux clang --disable-ssl	2m 7s
linux gcc c99	2m 9s
linux clang c99	2m 19s
linux gcc test 3.16	6m 38s
linux clang test 3.16 asan	10m 17s
linux gcc test --enable-shared	8m 25s
linux clang test --enable-shared	8m 9s
linux gcc test dpdk	6m 43s
linux clang test dpdk	6m 27s
linux gcc test -ljemalloc	6m 23s
linux clang test -ljemalloc	6m 34s
linux gcc 5.8 5.5 5.4 4.19	5m 1s
linux clang 5.8 5.5 5.4 4.19	5m 15s
linux gcc 4.14 4.9 4.4 3.16	4m 24s
linux clang 4.14 4.9 4.4 3.16	4m 28s
linux gcc afxdp 5.3	2m 46s
linux clang afxdp 5.3	3m 21s
linux gcc dpdk --enable-shared	3m 8s
linux clang dpdk --enable-shared	2m 59s
linux gcc dpdk-shared	2m 25s
linux clang dpdk-shared	2m 11s
linux gcc dpdk-shared --enable-shared	3m 8s
linux clang dpdk-shared --enable-shared	2m 57s
linux gcc m32 --disable-ssl	2m 9s
linux gcc deb	5m 31s
	2h 0m 53s

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