man: ip-macsec: fix gcm-aes-256 formatting issue

The 'ip link add' invocation template at the top of the ip-macsec man
page formats with a pair of extra double quotes:

   ip  link  add  link DEVICE name NAME type macsec [ [ address <lladdr> ]
   port PORT | sci <u64> ]  [  cipher  {  default  |  gcm-aes-128  |  gcm-
   aes-256"}][" icvlen ICVLEN ] [ encrypt { on | off } ] [ send_sci { on |

This is due to missing whitespace around the gcm-aes-256 identifier
in the source file.

Fixes: b16f525323357 ("Add support for configuring MACsec gcm-aes-256 cipher type.")
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: David Ahern <dsahern@gmail.com>
diff --git a/man/man8/ip-macsec.8 b/man/man8/ip-macsec.8
index 6739e51..bb81615 100644
--- a/man/man8/ip-macsec.8
+++ b/man/man8/ip-macsec.8
@@ -10,7 +10,7 @@
 |
 .BI sci " <u64>"
 ] [
-.BR cipher " { " default " | " gcm-aes-128 " | "gcm-aes-256" } ] ["
+.BR cipher " { " default " | " gcm-aes-128 " | " gcm-aes-256 " } ] ["
 .BI icvlen " ICVLEN"
 ] [
 .BR encrypt " { " on " | " off " } ] ["