net: clarify IP.IsGlobalUnicast docs
net: clarify IP.IsGlobalUnicast docs

Fixes #18181.

Change-Id: I5eed99dfb7b013aa4d4e668e95a97f5bb643d307
Reviewed-on: https://go-review.googlesource.com/34531
Run-TryBot: Mikio Hara <e2f4d2eec1d9a1f781345cdd7260d7d52e6468ae@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

polyverse-security/go,codestation/go,linux-on-ibm-z/go,cloudflare/go,CAFxX/go,polyverse-security/go,golang/go,vsekhar/elastic-go,cloudflare/go,golang/go,golang/go,Cofyc/go,josharian/go,derekmarcotte/go,nawawi/go,derekmarcotte/go,akutz/go,josharian/go,derekmarcotte/go,ImJasonH/go,josharian/go,CAFxX/go,josharian/go,golang/go,josharian/go,suncycheng/go,nawawi/go,golang/go,vsekhar/elastic-go,ImJasonH/go,linux-on-ibm-z/go,golang/go,ImJasonH/go,akutz/go,codestation/go,golang/go,derekmarcotte/go,nawawi/go,cloudflare/go,Cofyc/go,suncycheng/go,cloudflare/go,nawawi/go,derekmarcotte/go,vsekhar/elastic-go,CAFxX/go,polyverse-security/go,golang/go,vsekhar/elastic-go,CAFxX/go,ImJasonH/go,nawawi/go,polyverse-security/go,Cofyc/go,polyverse-security/go,akutz/go,akutz/go,suncycheng/go,derekmarcotte/go,derekmarcotte/go,CAFxX/go,vsekhar/elastic-go,ImJasonH/go,polyverse-security/go,linux-on-ibm-z/go,codestation/go,ImJasonH/go,linux-on-ibm-z/go,codestation/go,nawawi/go,Cofyc/go,suncycheng/go,polyverse-security/go,josharian/go,codestation/go,polyverse-security/go,vsekhar/elastic-go,Cofyc/go,akutz/go,ImJasonH/go,vsekhar/elastic-go,suncycheng/go,linux-on-ibm-z/go,Cofyc/go,codestation/go,linux-on-ibm-z/go,akutz/go,christopher-henderson/Go,cloudflare/go,josharian/go,suncycheng/go,cloudflare/go,cloudflare/go,Cofyc/go,codestation/go,akutz/go,CAFxX/go,ImJasonH/go,suncycheng/go,linux-on-ibm-z/go,codestation/go,linux-on-ibm-z/go,CAFxX/go,nawawi/go,Cofyc/go,suncycheng/go,josharian/go,akutz/go,derekmarcotte/go,CAFxX/go,cloudflare/go,vsekhar/elastic-go,nawawi/go