Make sure RBE socket address is under character limit

Check that socket address paths are less than the character limit - 2 since absolute paths are prefixed with //, which is included in the character limit.

b/308986536

Change-Id: I3055b8bb8cdae00aafd66c51fdc8421b9cc5f21f
diff --git a/ui/build/config.go b/ui/build/config.go
index 1a25397..78a1cc3 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -1387,7 +1387,9 @@
 }
 
 func (c *configImpl) rbeSockAddr(dir string) (string, error) {
-	maxNameLen := len(syscall.RawSockaddrUnix{}.Path)
+	// Absolute path socket addresses have a prefix of //. This should
+	// be included in the length limit.
+	maxNameLen := len(syscall.RawSockaddrUnix{}.Path) - 2
 	base := fmt.Sprintf("reproxy_%v.sock", rbeRandPrefix)
 
 	name := filepath.Join(dir, base)