netdev-linux: Fix unaligned access to rpl_rtnl_link_stats64. #2416

Job	Run time
dpdk gcc	5s
linux deb no dpdk	5m 48s
osx clang --disable-ssl	1m 28s
linux gcc --disable-ssl	2m 0s
linux clang --disable-ssl	2m 9s
linux gcc c99	1m 57s
linux clang c99	2m 10s
linux gcc test	7m 14s
linux clang test asan	12m 37s
linux clang test ubsan	8m 53s
linux gcc test --enable-shared	10m 3s
linux clang test --enable-shared	10m 0s
linux gcc test dpdk	7m 38s
linux clang test dpdk	7m 43s
linux gcc test -ljemalloc	7m 44s
linux clang test -ljemalloc	7m 49s
linux gcc --enable-afxdp	2m 2s
linux clang --enable-afxdp	1m 58s
linux gcc dpdk --enable-shared	3m 42s
linux clang dpdk --enable-shared	2m 57s
linux gcc dpdk-shared	2m 24s
linux clang dpdk-shared	2m 9s
linux gcc dpdk-shared --enable-shared	2m 52s
linux clang dpdk-shared --enable-shared	2m 48s
linux gcc m32 --disable-ssl	1m 55s
	1h 58m 5s

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