netdev-offload-dpdk: Fix flushing of a physdev. #2315

Job	Run time
dpdk gcc	3m 8s
linux rpm fedora	7m 30s
osx clang --disable-ssl	4m 0s
linux deb no dpdk	10m 8s
linux gcc --disable-ssl	4m 8s
linux clang --disable-ssl	3m 36s
linux gcc c99	4m 59s
linux clang c99	4m 9s
linux gcc test	11m 59s
linux clang test asan	24m 11s
linux clang test ubsan	13m 0s
linux gcc test --enable-shared	16m 56s
linux clang test --enable-shared	14m 36s
linux gcc test dpdk	12m 7s
linux clang test dpdk	10m 35s
linux gcc test -ljemalloc	13m 56s
linux clang test -ljemalloc	12m 47s
linux gcc --enable-afxdp	4m 34s
linux clang --enable-afxdp	4m 52s
linux gcc dpdk --enable-shared	6m 3s
linux clang dpdk --enable-shared	4m 37s
linux gcc dpdk-shared	3m 37s
linux clang dpdk-shared	3m 30s
linux gcc dpdk-shared --enable-shared	6m 58s
linux clang dpdk-shared --enable-shared	5m 54s
linux gcc m32 --disable-ssl	4m 14s
	3h 36m 4s

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