vmnet: work around skb_frag_t build failure for SLE15-SP2 and openSUSE-15.2

The kernels used in (upcoming) SLE15 SP2 and openSUSE Leap 15.2 are based
on upstream version 5.3 but have a backport of the skb_frag_t conversion to
bio_vec which reached mainline in v5.4-rc1. As we cannot easily check
availability compat_skb_frag_off() (which was also added in v5.4-rc1) and
have to resort to version check, add an exception for SLE15-SP2 and
openSUSE-15.2 kernels.

vmnet-only/userif.c

@@ -81,7 +81,9 @@ extern unsigned int  vnet_max_qlen;
 #   define skb_frag_page(frag) (frag)->page
 #   define skb_frag_size(frag) (frag)->size
 #endif
-#if COMPAT_LINUX_VERSION_CHECK_LT(5, 4, 0)
+#if COMPAT_LINUX_VERSION_CHECK_LT(5, 4, 0) && \
+    !(defined(CONFIG_SUSE_VERSION) && CONFIG_SUSE_VERSION == 15 && \
+      defined(CONFIG_SUSE_PATCHLEVEL) && CONFIG_SUSE_PATCHLEVEL >= 2)
 #   define skb_frag_off(frag) (frag)->page_offset
 #endif