pkg/vminfo: checking of syscalls that take string flags

[a-nogikh]

Currently, we determine whether a syscall should be enabled by looking only at the first string value in a list:

syzkaller/pkg/vminfo/syscalls.go

Line 365 in 375932c

v := str.Values[0]

This is not exactly right -- even if only some of the list values are supported, we should enable a syscall.

Cc @dvyukov