net: remove solaris tag from cgo

For now solaris port does not support cgo. Moreover, its system calls
and library interfaces are different from BSD.

Change-Id: Idb4fed889973368b35d38b361b23581abacfdeab
Reviewed-on: https://go-review.googlesource.com/3306Reviewed-by: Aram Hăvărneanu <aram@mgk.ro>

src/net/cgo_bsd.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build !netgo
-// +build darwin dragonfly freebsd solaris
+// +build darwin dragonfly freebsd
 
 package net