[ip6-address] inline very simple methods (#4519)

This commit inlines the very simple methods (containing a single
basic operation) in `Ip6::Address` class.

src/core/net/ip6_address.cpp

@@ -65,11 +65,6 @@ bool Address::IsLinkLocal(void) const
     return (mFields.m16[0] & HostSwap16(0xffc0)) == HostSwap16(0xfe80);
 }
 
-bool Address::IsMulticast(void) const
-{
-    return mFields.m8[0] == 0xff;
-}
-
 bool Address::IsLinkLocalMulticast(void) const
 {
     return IsMulticast() && (GetScope() == kLinkLocalScope);
@@ -149,16 +144,6 @@ bool Address::IsIidReserved(void) const
     return IsSubnetRouterAnycast() || IsReservedSubnetAnycast() || IsAnycastRoutingLocator();
 }
 
-const uint8_t *Address::GetIid(void) const
-{
-    return mFields.m8 + kInterfaceIdentifierOffset;
-}
-
-uint8_t *Address::GetIid(void)
-{
-    return mFields.m8 + kInterfaceIdentifierOffset;
-}
-
 void Address::SetIid(const uint8_t *aIid)
 {
     memcpy(mFields.m8 + kInterfaceIdentifierOffset, aIid, kInterfaceIdentifierSize);

src/core/net/ip6_address.hpp

@@ -142,7 +142,7 @@ public:
      * @retval FALSE  If the IPv6 address scope is not a multicast address.
      *
      */
-    bool IsMulticast(void) const;
+    bool IsMulticast(void) const { return mFields.m8[0] == 0xff; }
 
     /**
      * This method indicates whether or not the IPv6 address is a link-local multicast address.
@@ -276,7 +276,7 @@ public:
      * @returns A pointer to the Interface Identifier.
      *
      */
-    const uint8_t *GetIid(void) const;
+    const uint8_t *GetIid(void) const { return mFields.m8 + kInterfaceIdentifierOffset; }
 
     /**
      * This method returns a pointer to the Interface Identifier.
@@ -284,7 +284,7 @@ public:
      * @returns A pointer to the Interface Identifier.
      *
      */
-    uint8_t *GetIid(void);
+    uint8_t *GetIid(void) { return mFields.m8 + kInterfaceIdentifierOffset; }
 
     /**
      * This method sets the Interface Identifier.