sys/posix/socket: align struct sockaddr{,_storage}
sys/posix/socket: align struct sockaddr{,_storage}

Align the first member of `struct sockaddr` and
`struct sockaddr_storage` as `uint32_t` to elevate the alignment of the
structure to level of `uint32_t`. This is needed as
`struct sockaddr_in` uses an `uint32_t` to store the IPv4 address,
previously resulting in `struct sockaddr_in` currently having a greater
alignment requirement that `struct sockaddr_storage`.

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