Disable for loop when USE_RECVMSG is not defined

[trampen]

Following expresion should be run only when needed, when USE_RECVMSG or _WIN32 are defined

for (cmsghdr = CMSG_FIRSTHDR(&msghdr); cmsghdr != NULL ; cmsghdr = CMSG_NXTHDR(&msghdr, cmsghdr))

Runnig it for Android compilation where USE_RECVMSG is not defined cause infinite loop.