oeqa/selftest/gcc: Fix kex exchange identification error

while runnig oe-selftest for gcc, some of the testcases that need to be run on qemu
are not running due to below failures:
- kex_exchange_identification: read: Connection reset by peer^M
   Connection reset by 192.168.7.2 port 22^M
   ERROR: Couldn't create remote directory /tmp/runtest.3549814 on ssh

To resolve kex exchange identification error increased the MaxStartups.

(From OE-Core rev: 971d63d5b4982ce9ef4c4be742ba83a9708267da)

Signed-off-by: Harish Sadineni <Harish.Sadineni@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit df64d5ab6eb37dcdc2046f449ec539a3f4b985c8)
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/lib/oeqa/selftest/cases/gcc.py

@@ -83,6 +83,8 @@ class GccSelfTestBase(OESelftestTestCase, OEPTestResultTestCase):
             # validate that SSH is working
             status, _ = qemu.run("uname")
             self.assertEqual(status, 0)
+            qemu.run('echo "MaxStartups 75:30:100" >> /etc/ssh/sshd_config')
+            qemu.run('service sshd restart')
 
             return self.run_check(*args, ssh=qemu.ip, **kwargs)