rtmpdump: workaround kconfig issue by defaulting to gnutls

Otherwise we get:

package/openssl/Config.in:1:error: recursive dependency detected!
package/openssl/Config.in:1:    symbol BR2_PACKAGE_OPENSSL is selected by BR2_PACKAGE_GNUTLS
package/gnutls/Config.in:1:     symbol BR2_PACKAGE_GNUTLS is selected by BR2_PACKAGE_OPENSSL

Which is caused by lftp doing:

  select BR2_PACKAGE_GNUTLS if !BR2_PACKAGE_OPENSSL

And rtmpdump doing:

  select BR2_PACKAGE_OPENSSL if !BR2_PACKAGE_POLARSSL && !BR2_PACKAGE_GNUTLS

Which confuses kconfig. Work around it by swapping gnutls and openssl in
rtmpdump so it matches lftp.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>