Fix call to connect()

According to the manpage and the prototype the second argument to
connect(2) is a "const struct sockaddr*", so cast our protocol
specific type back to the super type.
This fixes compilation on musl-libc.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>