selftests/vsock: avoid false-positives when checking dmesg

selftests/vsock: avoid false-positives when checking dmesg

Sometimes VMs will have some intermittent dmesg warnings that are
unrelated to vsock. Change the dmesg parsing to filter on strings
containing 'vsock' to avoid false positive failures that are unrelated
to vsock. The downside is that it is possible for some vsock related
warnings to not contain the substring 'vsock', so those will be missed.

Fixes: a4a65c6fe08b ("selftests/vsock: add initial vmtest.sh for vsock")
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20251105-vsock-vmtest-dmesg-fix-v2-1-1a042a14892c@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>