Test Android network connectivity from abd shell

Usually network connectivity can be tested with ping and telnet. Android adb shell has ping but no telnet. But it has nc, which can be used in place of telnet.

# nc -z -v www.google.com 80
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f105.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f99.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f147.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f104.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f106.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f103.1e100.net
www.l.google.com [74.125.73.105] 80 (www) open
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# nc -z -v -w 5 www.google.com 81
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f99.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f147.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f106.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f105.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f104.1e100.net
DNS fwd/rev mismatch: www.l.google.com != tul01m01-in-f103.1e100.net
www.l.google.com [74.125.73.99] 81 (?) : Connection timed out
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# nc -h
[v1.10]
connect to somewhere:	nc [-options] hostname port[s] [ports] ... 
listen for inbound:	nc -l -p port [-options] [hostname] [port]
options:
	-g gateway		source-routing hop point[s], up to 8
	-G num			source-routing pointer: 4, 8, 12, ...
	-h			this cruft
	-i secs			delay interval for lines sent, ports scanned
	-l			listen mode, for inbound connects
	-n			numeric-only IP addresses, no DNS
	-o file			hex dump of traffic
	-p port			local port number
	-r			randomize local and remote ports
	-s addr			local source address
	-u			UDP mode
	-v			verbose [use twice to be more verbose]
	-w secs			timeout for connects and final net reads
	-z			zero-I/O mode [used for scanning]
port numbers can be individual or ranges: lo-hi [inclusive]
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