[posix-netif] remove IFA_RT_PRIORITY definition (#7635)
`IFA_RT_PRIORITY` not defined basically means that the feature is not
present. Defining it to 9 does not make it effective.
This commit removes the `IFA_RT_PRIORITY` definition so that it would
not compile on platforms that do not support `IFA_RT_PRIORITY`.
diff --git a/src/posix/platform/netif.cpp b/src/posix/platform/netif.cpp
index 04a80a9..0ecb888 100644
--- a/src/posix/platform/netif.cpp
+++ b/src/posix/platform/netif.cpp
@@ -322,10 +322,6 @@
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wcast-align"
-#if !defined(IFA_RT_PRIORITY)
-#define IFA_RT_PRIORITY 9
-#endif
-
void AddRtAttr(struct nlmsghdr *aHeader, uint32_t aMaxLen, uint8_t aType, const void *aData, uint8_t aLen)
{
uint8_t len = RTA_LENGTH(aLen);