Make use sram default in some cores that have this as an option

true is what end users would expect most of the time.  false is only for advanced use cases.

src/BizHawk.Emulation.Cores/Consoles/Magnavox/Odyssey2/O2Hawk.ISettable.cs

@@ -64,7 +64,7 @@ namespace BizHawk.Emulation.Cores.Consoles.O2Hawk
 		{
 			[DisplayName("Use Existing SaveRAM")]
 			[Description("When true, existing SaveRAM will be loaded at boot up")]
-			[DefaultValue(false)]
+			[DefaultValue(true)]
 			public bool Use_SRAM { get; set; }
 
 			public O2SyncSettings Clone()

src/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawkLink/GBHawkLink.ISettable.cs

@@ -126,7 +126,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawkLink
 
 			[DisplayName("Use Existing SaveRAM")]
 			[Description("When true, existing SaveRAM will be loaded at boot up")]
-			[DefaultValue(false)]
+			[DefaultValue(true)]
 			public bool Use_SRAM { get; set; }
 
 			[JsonIgnore]

src/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawkLink3x/GBHawkLink3x.ISettable.cs

@@ -143,7 +143,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawkLink3x
 
 			[DisplayName("Use Existing SaveRAM")]
 			[Description("When true, existing SaveRAM will be loaded at boot up")]
-			[DefaultValue(false)]
+			[DefaultValue(true)]
 			public bool Use_SRAM { get; set; }
 
 			[JsonIgnore]

src/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawkLink4x/GBHawkLink4x.ISettable.cs

@@ -172,7 +172,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawkLink4x
 
 			[DisplayName("Use Existing SaveRAM")]
 			[Description("When true, existing SaveRAM will be loaded at boot up")]
-			[DefaultValue(false)]
+			[DefaultValue(true)]
 			public bool Use_SRAM { get; set; }
 
 			[JsonIgnore]

src/BizHawk.Emulation.Cores/Consoles/Sega/GGHawkLink/GGHawkLink.ISettable.cs

@@ -57,7 +57,7 @@ namespace BizHawk.Emulation.Cores.Sega.GGHawkLink
 
 			[DisplayName("Use Existing SaveRAM")]
 			[Description("When true, existing SaveRAM will be loaded at boot up")]
-			[DefaultValue(false)]
+			[DefaultValue(true)]
 			public bool Use_SRAM { get; set; }
 
 			public GGLinkSyncSettings Clone()