uhttpd: add support to generate EC keys

This adds the key_type and ec_curve options to enable the generation of
EC keys during initialization, using openssl or the new options added to
px5g.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>

package/network/services/uhttpd/files/uhttpd.config

@@ -118,9 +118,17 @@ config cert defaults
 	# Validity time
 	option days		730
 
+	# key type: rsa or ec
+	option key_type		rsa
+
 	# RSA key size
 	option bits		2048
 
+	# EC curve name
+	# Curve names vary between mbedtls/px5g and openssl
+	# P-256 or P-384 are guaranteed to work
+	option ec_curve		P-256
+
 	# Location
 	option country		ZZ
 	option state		Somewhere