There appear to be devices out there which send only their
first descriptor in response to a discovery packet for
`ssdp:all`, for example the Sagemcom FAST3890V3 only sends
urn:schemas-wifialliance-org:device:WFADevice:1
Send both ssdp:all and a discovery frame for
InternetGatewayDevice specifically.
Updates https://github.com/tailscale/tailscale/issues/3557
Signed-off-by: Denton Gentry <dgentry@tailscale.com>