Previously v2ray can not be built on illumos due to following reasons:
1. missing build tags in transport/internet/sockopt_other.go
2. many definitions in syscall does not exist on illumos
This commit addresses these problems by adding missing build tags, and
updates those missing syscall deps on illumos to use x/sys/unix.
- transparent proxy (pf rdr) in IPv4 environment
- support both tcp and udp
- enable TCP_FASTOPEN, SO_REUSEPORT_LB, SO_REUSEADDR
- sockopt:mark is mapped to SO_USER_COOKIE
