maint: Ignore ivshmem binaries

Commit a75eb03b added ivshmem-client and ivshmem-server binaries,
but did not mark them for exclusion in .gitignore.
Signed-off-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

.gitignore

@@ -24,6 +24,8 @@
 /*-darwin-user
 /*-linux-user
 /*-bsd-user
+/ivshmem-client
+/ivshmem-server
 /libdis*
 /libuser
 /linux-headers/asm