[submodule] Update sonic-linux-kernel submodule

Update sonic-linux-kernel submodule pointer to include the following:
* [Mellanox] Add new kernel patches from HW-MGMT package V.7.0020.3005 ([sonic-net#287](sonic-net/sonic-linux-kernel#287))
* [patch] mlxsw: i2c: Prevent transaction execution for special chip ([sonic-net#279](sonic-net/sonic-linux-kernel#279))
* [sflow + dropmon] added missing patch for the sFlow + dropmon feature. ([sonic-net#281](sonic-net/sonic-linux-kernel#281))
* [sflow + dropmon] added patches for the sFlow + dropmon feature. ([sonic-net#276](sonic-net/sonic-linux-kernel#276))

Signed-off-by: dprital <[email protected]>