linux-user: Check lock_user result for ip_mreq_source sockopts

In do_setsockopt(), the code path for the options which take a struct
ip_mreq_source (IP_BLOCK_SOURCE, IP_UNBLOCK_SOURCE,
IP_ADD_SOURCE_MEMBERSHIP and IP_DROP_SOURCE_MEMBERSHIP) fails to
check the return value from lock_user().  Handle this in the usual
way by returning -TARGET_EFAULT.

(In practice this was probably harmless because we'd pass a NULL
pointer to setsockopt() and the kernel would then return EFAULT.)

Fixes: Coverity CID 1459987
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210809155424.30968-1-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>