Change network_priority from a double to an enum.

It can only be one of four possible values, so it never made sense
for it to be a double. Other than the fact that its neighbor
bitrate_priority is a double, and they're both defined as the same enum
in the web spec. However, while bitrate_priority being a double
offers more flexibility than the web spec, network_priority being a
double is only confusing.

Bug: webrtc:5658
Change-Id: I0784c116f3260c4b3a8b99a3cd85c8d66017e46f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168840
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Taylor <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30685}

sdk/objc/api/peerconnection/RTCRtpEncodingParameters.h

@@ -14,6 +14,14 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+/** Corresponds to webrtc::Priority. */
+typedef NS_ENUM(NSInteger, RTCPriority) {
+  RTCPriorityVeryLow,
+  RTCPriorityLow,
+  RTCPriorityMedium,
+  RTCPriorityHigh
+};
+
 RTC_OBJC_EXPORT
 @interface RTCRtpEncodingParameters : NSObject
 
@@ -52,7 +60,7 @@ RTC_OBJC_EXPORT
 @property(nonatomic, readonly, nullable) NSNumber *ssrc;
 
 /** The relative DiffServ Code Point priority. */
-@property(nonatomic, assign) double networkPriority;
+@property(nonatomic, assign) RTCPriority networkPriority;
 
 - (instancetype)init NS_DESIGNATED_INITIALIZER;