netdev-linux: Fix unaligned access to rpl_rtnl_link_stats64. #3049

Job	Run time
dpdk gcc	10s
osx clang --disable-ssl	1m 32s
linux rpm fedora	4m 4s
linux deb no dpdk	6m 15s
clang-analyze	9m 26s
linux gcc --disable-ssl	2m 21s
linux clang --disable-ssl	2m 28s
linux gcc c99	2m 23s
linux clang c99	2m 19s
linux gcc test	8m 29s
linux clang address,undefined test	15m 53s
linux gcc test --enable-shared	11m 28s
linux clang test --enable-shared	11m 38s
linux gcc check check-dpdk dpdk	18m 33s
linux clang check check-dpdk dpdk	17m 53s
linux gcc test -ljemalloc	9m 0s
linux clang test -ljemalloc	8m 46s
linux gcc --enable-afxdp	2m 21s
linux clang --enable-afxdp	2m 34s
linux gcc dpdk --enable-shared	3m 24s
linux clang dpdk --enable-shared	3m 37s
linux gcc dpdk-shared	2m 40s
linux clang dpdk-shared	2m 41s
linux gcc dpdk-shared --enable-shared	3m 41s
linux clang dpdk-shared --enable-shared	3m 21s
linux gcc m32 --disable-ssl	2m 21s
linux gcc check-ovsdb-cluster	6m 38s
linux gcc check-kernel -100	9m 15s
linux gcc check-kernel 100-	9m 17s
linux clang address,undefined check-kernel -100	11m 26s
linux clang address,undefined check-kernel 100-	11m 37s
linux gcc check-offloads -100	9m 5s
linux gcc check-offloads 100-	7m 48s
linux gcc dpdk check-system-userspace	10m 47s
linux clang address,undefined dpdk check-system-userspace	14m 24s
linux gcc dpdk check-system-tso	10m 23s
linux gcc dpdk check-afxdp	11m 24s
	4h 31m 22s

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