package/libnice: add optional dependency to openssl

package/libnice: add optional dependency to openssl

Support for OpenSSL was added in version 0.1.15:
https://lists.freedesktop.org/archives/nice/2018-December/001443.html

With the option of using OpenSSL as a crypto provider, we can't keep
GnuTLS as the default, because using:

       select BR2_PACKAGE_GNUTLS if !BR2_PACKAGE_OPENSSL

causes a Kconfig circular dependency:

package/openssl/Config.in:4:error: recursive dependency detected!
package/openssl/Config.in:4:	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

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
[Thomas: pass --with-crypto-library argument]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>